Inductive displacement sensors

ABSTRACT

A target for an inductive displacement sensor is provided, including a plurality of conductive patterns distributed along a zone having a dimension Dtot in a direction, the patterns being defined by the overlay of at least a first set of elementary periodic patterns having a period approximately equal to Dtot/N, including N first elementary conductive patterns of a dimension approximately equal to Dtot/2N in the direction, regularly distributed along the zone, and of a second set of elementary periodic patterns having a period approximately equal to Dtot/(N+r), including N+r second elementary patterns of a dimension approximately equal to Dtot/2(N+r) in the direction, regularly distributed along the zone, where N is an integer greater than or equal to 2 and r is a positive integer, different to zero and less than or equal to N−1, wherein first and second elementary conductive patterns overlap at least partially.

FIELD

The present application relates to the field of inductive measurement ofdisplacement of one mechanical part with respect to another. The terminductive measurement denotes herein the measurement of alternatingelectromagnetic fields, by means of electrical coils. More specificallybut not restrictively, the present application relates to the technicalsub-field of eddy-current sensors, wherein an electromagnetic fieldgenerated by an inductor is established differently according to thepresence and the arrangement of movable (with respect to the inductor)conductive parts in the vicinity of the inductor. Such electromagneticphenomena become exploitable for instrumentation purposes when certainelectrical frequencies of the electromagnetic field adopt sufficientlylarge values, this concept of largeness being determined by a pluralityof parameters such as the geometric dimensions of the conductive parts,the electrical and magnetic properties thereof, the temperature thereof,etc. The term displacement measurement denotes herein the estimation ofinformation relating to the position, speed, acceleration or any othercharacteristic quantity of the displacements of the conductive part withrespect to the inductor or to the inductor reference frame. Asdisplacements, equally well angular (rotation about an axis), linear(translation along an axis) displacements, or any combination of suchdisplacements with one another or along separate axes are taken intoconsideration. More particularly but not restrictively, the presentapplication relates to the technical sub-fields of inductive positionsensors, inductive speed sensors and/or inductive acceleration sensors.

DESCRIPTION OF THE PRIOR ART

An inductive displacement sensor typically comprises a transducer (forexample rigidly connected to a measurement reference frame, also knownas a frame), and a target (for example rigidly connected to a movablemechanical part with respect to the measurement reference frame). Thetarget is placed away from the transducer, and is not in contact (eithermechanically or electrically) with the transducer (contactlessmeasurement). The transducer includes a primary winding, or inductor,suitable for producing an alternating electromagnetic field, and atleast one secondary winding at the terminals whereof an alternatingvoltage is induced, also referred to as electromotive force or EMF, inthe presence of the electromagnetic field produced by the primarywinding. The target is a partially or fully conductive element, alsoreferred to as a coupling armature, the presence and/or movement whereofin front of the transducer modifies the coupling between the primarywinding and the secondary winding. It should be noted that the effect ofthe target on the coupling between the primary winding and the secondarywinding is dependent on the position of the target with respect to thetransducer, but also on the speed thereof with respect to thetransducer.

The electromagnetic field distribution is thus formed spatiallyaccording to the position and the relative displacement of the targetwith respect to the transducer. During a displacement of the mechanicalpart, the spatial distribution of the electromagnetic field changes, andtherefore the EMF induced in the secondary winding also changes. Theanalysis of the EMF induced, at the terminals of the secondary winding,by the electromagnetic field produced by the primary winding, makes itpossible to estimate the position and/or the displacement of the targetwith respect to the secondary winding of the transducer. Moreparticularly but not restrictively, the temporal variations of the EMFamplitude at the terminals of the secondary winding make it possible toestimate the position, speed and/or acceleration of the target withrespect to the transducer.

It is specified that, herein and hereinafter in the present application,the term electromotive force range amplitude at the terminals of thesecondary winding refers to the instantaneous value adopted by a limitedfrequency content signal, for example in a frequency band between −Δfand +Δf about the excitation frequency (i.e. the frequency of thealternating voltage applied at the terminals of the primary winding),where Δf could for example adopt a value between 100 Hz and 100 kHz,carrying the information or a part of the characteristic information ofthe mechanical displacement. This signal is contained in theelectromotive force, modulated at the excitation frequency and/or theharmonics thereof. It can be obtained by means of a frequencytransposition and filtering method, and more specifically by means ofbase band transposition and filtering. A preferred example of such amethod consists of carrying out synchronous demodulation of the(modulated) electromotive force using a synchronous excitation frequencysignal, and wherein the electrical phase has been chosen to meetspecific criteria, for example to maximize the signal obtained at thedemodulation output. An alternative method consists of computing themodulus of the signal after synchronous demodulation, which involves theadvantage and disadvantage of not setting an electrical demodulationphase. It is also specified that the amplitude of the electromagneticforce is a preferred measurement quantity for the implementation of adisplacement measurement with the sensors according to the invention,but that it is in no way exclusive from further electrical measurementquantities such as the phase, frequency, or the electrical power at thesecondary winding when a load of finite value is connected to theterminals of the secondary winding (load adaptation).

Examples of inductive displacement sensors, and more particularly ofeddy-current position sensors have been described in the patentEP0182085.

However, known inductive displacement sensors involve various drawbacks.In particular, known sensors are relatively sensitive to assemblyinaccuracies (misalignment, inclination and/or target/transducerdistance), as well as the presence of conductive parts in the vicinityof the measurement zone, which poses problems for industrial use.Problems associated with the lack of linearity of the sensor responsemay also arise. Furthermore, the precision and robustness of theestimation of the position and/or displacement of the target in knownsensors would merit being improved. Moreover, it would be desirable tobe able to increase the extent of the measurement range of some types ofknown sensors. In addition, one drawback of known sensors is that theyare relatively fragile, which poses problems in some types ofapplication, particularly in an industrial environment.

It would be desirable to be able to have inductive displacement sensorsremedying all or some of the drawbacks of known sensors.

SUMMARY

As such, one embodiment envisages a target for an inductive displacementsensor, comprising a plurality of conductive patterns distributed alonga zone having a dimension D_(tot) in a direction, said patterns beingdefined by the overlay of at least a first set of elementary periodicpatterns having a period approximately equal to D_(tot)/N, including Nfirst elementary conductive patterns of a dimension approximately equalto D_(tot)/2N in said direction, regularly distributed along said zone,and of a second set of elementary periodic patterns having a periodapproximately equal to D_(tot)/(N+r), including N+r second elementarypatterns of a dimension approximately equal to D_(tot)/2(N+r) in saiddirection, regularly distributed along said zone, where N is an integergreater than or equal to 2 and r is a positive integer, different tozero and less than or equal to N−1, wherein first and second elementaryconductive patterns overlap at least partially.

According to one embodiment, the first and second elementary conductivepatterns have respectively the shape of portions of overlaid first andsecond strips parallel with said direction.

According to one embodiment, the first and second strips are ofapproximately identical widths.

According to one embodiment, the first and second strips are of separatewidths, the first strip being at least two times wider than the secondstrip.

According to one embodiment, N is an even number.

According to one embodiment, said patterns are defined by the overlay ofthe first and second sets of periodic elementary patterns, and of athird set of periodic elementary patterns having a period approximatelyequal to D_(tot)/(N+r), comprising N+r third elementary patterns of adimension approximately equal to D_(tot)/2(N+r) in said direction,regularly distributed along said zone with an offset of approximatelyD_(tot)/2(N+r) with respect to the elementary patterns of the second setof periodic patterns, first and third elementary conductive patternsoverlapping at least partially.

According to one embodiment, the first, second and third elementarypatterns have respectively the shape of portions of first, second andthird strips parallel with said direction, the first and second strips,on one hand, and the first and third strips, on the other, beingoverlaid, and the second and third strips being approximately of thesame width less than the width of the first strip.

According to one embodiment, the direction is a circular direction.

According to one embodiment, the dimension D_(tot) is an angulardimension equal to 360°.

According to one embodiment, r is equal to 1.

A further embodiment envisages a transducer for an inductivedisplacement sensor, comprising: a primary winding; a first set of atleast two secondary windings each comprising N first turns of the samewinding direction or 2N first turns of alternating winding directions,regularly distributed along a zone having a dimension D_(tot) in adirection, each first turn having a dimension in said directionapproximately equal to D_(tot)/2N; and a second set of at least twosecondary windings each comprising N+r second turns of the same windingdirection or 2(N+r) second turns of alternating winding directions,regularly distributed along said zone, each second turn having adimension in said direction approximately equal to D_(tot)/2(N+r), whereN is an integer greater than or equal to 2 and r is a positive integer,different to zero and less than or equal to N−1, wherein first andsecond turns overlap at least partially.

According to one embodiment, the first and second turns haverespectively the shape of portions of overlaid first and second stripsparallel with said direction.

According to one embodiment, the transducer further comprises a thirdset of at least two secondary windings each comprising N+r third turnsof the same winding directions or 2(N+r) turns of alternating windingdirections, regularly distributed along said zone with an offset ofapproximately D_(tot)/2(N+r) with respect to the second set, each thirdturn having a dimension approximately equal to D_(tot)/2(N+r) in saiddirection, and first and second turns overlapping at least partially.

According to one embodiment, the first, second and third turns haverespectively the shape of portions of first, second and third stripsparallel with said direction, the first and second strips being overlaidand the first and third strips being overlaid.

According to one embodiment, the second and third secondary windings areconnected in series.

According to one embodiment, the serial connection point of the secondand third secondary windings is connected to an electrical connectionterminal.

A further embodiment envisages an inductive displacement sensor,comprising a transducer of the type mentioned above, and a target of thetype mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

These features and advantages, along with others, will be described indetail in the following description of particular embodiments givennon-restrictively with reference to the attached figures wherein:

FIGS. 1A and 1B are respectively a front view and a profile viewschematically representing an example of an inductive angulardisplacement sensor;

FIG. 2 is a diagram schematically illustrating the operation of thesensor in FIG. 1;

FIGS. 3A and 3B are front views schematically representing a transducerand a target of a further example of an inductive angular displacementsensor;

FIG. 4 is a diagram schematically illustrating the operation of thesensor in FIGS. 3A and 3B;

FIG. 5 is a front view schematically representing a transducer of afurther example of an inductive angular displacement sensor;

FIG. 6 is a diagram schematically illustrating the operation of thesensor in FIG. 5;

FIG. 7 is a front view schematically representing a transducer of afurther example of an inductive angular displacement sensor;

FIG. 8 is a diagram schematically illustrating the operation of thesensor in FIG. 7;

FIG. 9A is a diagram representing the expected theoretical progressionof output signals of an inductive angular displacement sensor;

FIG. 9B is a diagram representing the actual progression, typicallyobtained in practice, of the output signals of an inductive angulardisplacement sensor;

FIG. 10 is a diagram representing, for a plurality of distincttarget-transducer distances, the progression of an output signal of aninductive angular displacement sensor;

FIG. 11 is a diagram representing the progression, according to thetarget-transducer distance, of the linearity error of an output signalof an inductive angular displacement sensor;

FIGS. 12A to 12D are cross-sectional views schematically illustratingfour examples of embodiments of an inductive angular displacementsensor;

FIG. 13A is a diagram representing, for the four examples of sensors inFIGS. 12A to 12D, the progression, according to the target-transducer,of the linearity error of an output signal of the sensor;

FIG. 13B is a diagram representing the progression of the optimaltarget-transducer distance in terms of linearity according to aparameter of an example of an inductive displacement sensor;

FIG. 13C is a diagram representing the progression of the optimaltarget-transducer distance in terms of linearity according to aparameter of a further example of an inductive displacement sensor;

FIG. 14 is a front view representing an example of a field confinementpart of an example of an embodiment of an inductive angular displacementsensor;

FIG. 15 is a front view representing a further example of a fieldconfinement part of an example of an embodiment of an inductive angulardisplacement sensor;

FIGS. 16A and 16B are front views schematically representing twoexamples of embodiments of a target of an inductive angular displacementsensor;

FIG. 17 is a diagram representing the progression, in an inductiveangular displacement sensor, of the optimal target-distances in terms oflinearity, according to a shape parameter of a pattern of the target;

FIG. 18A is a front view schematically and partially representing threeexamples of embodiments of a target of an inductive angular displacementsensor;

FIG. 18B is a front view schematically and partially representing anexample of an embodiment of a secondary winding of a transducer suitablefor operating in cooperation with the targets in FIG. 18A;

FIG. 19 is a diagram representing the progression, in an inductiveangular displacement sensor, of the optimal target-transducer distancein terms of linearity, according to a further shape parameter of apattern of the target;

FIG. 20A is a front view schematically representing an example of atransducer of an inductive angular displacement sensor;

FIG. 20B is a front view schematically representing an example of atransducer of an inductive linear displacement sensor;

FIG. 20C is a front view schematically representing an example of anembodiment of a transducer of an inductive angular displacement sensor;

FIG. 20D is a front view schematically representing an example of anembodiment of a transducer of an inductive linear displacement sensor;

FIG. 20E is a small-signal electrical representation of the behavior ofthe transducer in FIG. 20D;

FIGS. 21A and 21B are front views schematically representing an exampleof an embodiment of a transducer of an inductive angular displacementsensor;

FIGS. 22A and 22B are front views schematically representing a furtherexample of an embodiment of a transducer of an inductive angulardisplacement sensor;

FIG. 23 is a front view schematically representing a target of anexample of inductive angular displacement sensor;

FIG. 24 is a diagram schematically representing the progression ofmeasurement signals of the sensor in FIG. 23;

FIG. 25 is a front view schematically representing a target of anexample of an embodiment of an inductive angular displacement sensor;

FIG. 26 is a front view schematically representing a target of analternative embodiment of an inductive angular displacement sensor;

FIGS. 27A to 27C are front views schematically representing a furtheralternative embodiment of an inductive angular displacement sensor;

FIG. 28 is a perspective view representing an example of an embodimentof an inductive angular displacement sensor target; and

FIG. 29 is a perspective view representing a further example of anembodiment of an inductive angular displacement sensor target.

DETAILED DESCRIPTION

For the purposes of clarity, the same elements have been denoted withthe same references in the various figures and, furthermore, the variousfigures are not plotted to scale. Moreover, hereinafter in thedescription, unless specified otherwise, the terms “approximately”,“substantially”, “around”, “of the order of”, “practically”, etc., mean“within 20% and preferably within 5%”, or “within 5° and preferablywithin 2°” when they relate to angular distances, and directionalreferences such as “vertical”, “horizontal”, “lateral”, “below”,“above”, “top”, “bottom”, etc., apply to device oriented in the mannerillustrated in the corresponding views, it being understood that, inpractice, these devices may be oriented differently.

Particular focus is placed on the inductive measurement of displacementof one mechanical part with respect to another. The term inductivemeasurement denotes herein the measurement of alternatingelectromagnetic fields, by means of electrical coils. More specificallybut not restrictively, the present application relates to the technicalsub-field of eddy-current sensors, wherein an electromagnetic fieldgenerated by an inductor is established differently according to thepresence and the arrangement of movable (with respect to the inductor)conductive parts in the vicinity of the inductor. Such electromagneticphenomena become exploitable for instrumentation purposes when certainelectrical frequencies of the electromagnetic field adopt sufficientlylarge values, this concept of largeness being determined by a pluralityof parameters such as the geometric dimensions of the conductive parts,the electrical and magnetic properties thereof, the temperature thereof,etc. The term displacement measurement denotes herein the estimation ofinformation relating to the position, speed, acceleration or any othercharacteristic quantity of the displacements of the conductive part withrespect to the inductor or to the inductor reference frame. Asdisplacements, equally well angular (rotation about an axis), linear(translation along an axis) displacements, or any combination of suchdisplacements with one another or along separate axes are taken intoconsideration. More particularly but not restrictively, the presentapplication relates to the technical sub-fields of inductive positionsensors, inductive speed sensors and/or inductive acceleration sensors.

An inductive displacement sensor typically comprises a transducer (forexample rigidly connected to a measurement reference frame, also knownas a frame), and a target (for example rigidly connected to a movablemechanical part with respect to the measurement reference frame). Thetarget is placed away from the transducer, and is not in contact (eithermechanically or electrically) with the transducer (contactlessmeasurement). The transducer includes a primary winding, or inductor,suitable for producing an alternating electromagnetic field, and atleast one secondary winding at the terminals whereof an alternatingvoltage is induced, also referred to as electromotive force or EMF, inthe presence of the electromagnetic field produced by the primarywinding. The target is a partially or fully conductive element, alsoreferred to as a coupling armature, the presence and/or movement whereofin front of the transducer modifies the coupling between the primarywinding and the secondary winding. It should be noted that the effect ofthe target on the coupling between the primary winding and the secondarywinding is dependent on the position of the target with respect to thetransducer, but also on the speed thereof with respect to thetransducer.

The electromagnetic field distribution is thus formed spatiallyaccording to the position and the relative displacement of the targetwith respect to the transducer. During a displacement of the mechanicalpart, the spatial distribution of the electromagnetic field changes, andtherefore the EMF induced in the secondary winding also changes. Theanalysis of the EMF induced, at the terminals of the secondary winding,by the electromagnetic field produced by the primary winding, makes itpossible to estimate the position and/or the displacement of the targetwith respect to the secondary winding of the transducer. Moreparticularly but not restrictively, the temporal variations of the EMFamplitude at the terminals of the secondary winding make it possible toestimate the position, speed and/or acceleration of the target withrespect to the transducer.

It is specified that, herein and hereinafter in the present application,the term electromotive force range amplitude at the terminals of thesecondary winding refers to the instantaneous value adopted by a limitedfrequency content signal, for example in a frequency band between −Δfand +Δf about the excitation frequency (i.e. the frequency of thealternating voltage applied at the terminals of the primary winding),where Δf could for example adopt a value between 100 Hz and 100 kHz,carrying the information or a part of the characteristic information ofthe mechanical displacement. This signal is contained in theelectromotive force, modulated at the excitation frequency and/or theharmonics thereof. It can be obtained by means of a frequencytransposition and filtering method, and more specifically by means ofbase band transposition and filtering. A preferred example of such amethod consists of carrying out synchronous demodulation of the(modulated) electromotive force using a synchronous excitation frequencysignal, and wherein the electrical phase has been chosen to meetspecific criteria, for example to maximize the signal obtained at thedemodulation output. An alternative method consists of computing themodulus of the signal after synchronous demodulation, which involves theadvantage and disadvantage of not setting an electrical demodulationphase. It is also specified that the amplitude of the electromagneticforce is a preferred measurement quantity for the implementation of adisplacement measurement with the sensors according to the invention,but that it is in no way exclusive from further electrical measurementquantities such as the phase, frequency, or the electrical power at thesecondary winding when a load of finite value is connected to theterminals of the secondary winding (load adaptation).

Examples of inductive displacement sensors, and more particularly ofeddy-current position sensors have been described in the patentEP0182085.

However, known inductive displacement sensors involve various drawbacks.In particular, known sensors are relatively sensitive to assemblyinaccuracies (misalignment, inclination and/or target/transducerdistance), as well as the presence of conductive parts in the vicinityof the measurement zone, which poses problems for industrial use.Problems associated with the lack of linearity of the sensor responsemay also arise. Furthermore, the precision and robustness of theestimation of the position and/or displacement of the target in knownsensors would merit being improved. Moreover, it would be desirable tobe able to increase the extent of the measurement range of some types ofknown sensors. In addition, one drawback of known sensors is that theyare relatively fragile, which poses problems in some types ofapplication, particularly in an industrial environment.

It would be desirable to be able to have inductive displacement sensorsremedying all or some of the drawbacks of known sensors.

Very particular focus is placed herein on angular displacement sensors,and more specifically on angular displacement sensors having anapproximately planar general shape, for example sensors having a generaldisk shape, sensors having a circular annular strip shape having anangular aperture less than or equal to 360°. It will be understoodhowever upon reading the following that all the examples of embodiments,embodiments and alternative embodiments described in the presentapplication can be adapted to further types of inductive displacementsensors, for example inductive linear displacement sensors of the typedescribed in the patent EP0182085 mentioned above. The adaptation of theexamples of embodiments described in the present application to furthertypes of inductive displacement sensors is within the grasp of thoseskilled in the art and therefore will not be detailed hereinafter.

By way of an illustrative but non-restrictive example, the inductivesensors described in the present application and illustrated in thefigures have characteristic dimensions (diameter for angular sensors andwidth for linear sensors) between 5 mm and 200 mm, and preferablybetween 40 mm and 50 mm.

FIGS. 1A and 1B are respectively a front view and a profile viewschematically representing an example of a planar type inductive angularposition sensor 100, having a general disk shape.

The sensor 100 comprises a transducer 110 including a primary conductivewinding 101 and a secondary conductive winding 103. In FIG. 1B, theprimary and secondary windings of the transducer 110 have not beendetailed. Preferably, the primary winding 101 comprises twoapproximately circular, concentric and coplanar conductive turns orloops 101 a and 101 b, of opposite winding directions and separateradii. Each turn 101 a, 101 b of the primary winding 101 comprises atleast one revolution, preferably a plurality of revolutions. The turns101 a and 101 b are preferably connected in series so as to be traversedby currents of the same intensity but in opposite flow directions, butcan optionally be connected in parallel so as to see the same voltage atthe terminals thereof (applied preferably such that the current flowdirection in the two turns are opposite). An advantage of the example ofprimary winding arrangement in FIG. 1 is that it makes it possible toproduce a substantially uniform excitation field in the annular stripsituated between the two turns, and substantially zero outside thisstrip. Alternatively, the primary winding 101 can include a single turn(with one or a plurality of revolutions). More generally, the primarywinding 101 can include one or a plurality of concentric turns (with oneor a plurality of revolutions each) arranged so as to generate anelectromagnetic field in the measurement zone of the transducer. Theembodiments described are not restricted to these particulararrangements of the primary winding.

In the example represented, the secondary winding 103 consists of aconductive turn or loop arranged spatially in the shape of a circularannular strip situated between the turns 101 a and 101 b. The winding103 is for example situated approximately in the same plane as the turns101 a and 101 b, or in a substantially parallel plane.

In this example, in a front view, the turn 103 substantially follows thecontour of an angular sector having an angular aperture α of the annularstrip defined by the turns 101 a and 101 b. The turn 103 particularlycomprises radial portions and ortho-radial portions of the contour ofthe annular strip portion. Such a winding enables an angular positionmeasurement over a range of α°. In the example represented, the angularaperture α of the turn 103 is approximately equal to 30°. Theembodiments described are however not restricted to this particularcase. Alternatively, the angle α can adopt any value between 0 and 180°.The turn 103 preferably comprises a single revolution but can optionallycomprise a plurality of revolutions. The primary 101 and secondary 103windings are for example arranged in and on the same dielectricsubstrate (not shown) in the form of a wafer of some micrometers to somemillimeters in thickness, for example a PCB (“Printed Circuit Board”)type substrate.

The sensor 100 further comprises a target 111 comprising a conductivepattern 107, situated at a distance different to zero from thetransducer and suitable for moving with respect to the transducer. InFIG. 1A, only the conductive part 107 of the target has beenrepresented. In this example, the conductive pattern 107 of the target111 has substantially the same shape as the annular strip portiondefined by the pattern of the turn 103 of the transducer. The target isrotatably mounted about an axis Z orthogonal to the plane of thetransducer passing through the center of the turns 101 a and 101 b, suchthat, when the target rotates by an angle 2α about the axis Z, theconductive pattern 107 (having the angular aperture α), coversapproximately entirely and then uncovers approximately entirely thesurface of the annular strip defined by the turn of the secondarywinding 103 of the transducer. By way of non-restrictive example, thetarget can consist of a plate made of a dielectric material, for examplein the shape of a disk, wherein one face oriented towards the transduceris partially coated with a layer of a conductive material, optionallymagnetic, for example a metal layer, for example a layer of iron, steel,aluminum, copper, etc., forming the conductive pattern 107.Alternatively, the target can consist solely of a portion of metal platecut to the shape of the conductive pattern 107, mounted by any suitablemeans so as to be able to move in rotation with respect to thetransducer above the portion of annular strip defined by the turns 101 aand 101 b.

The operation of the sensor 100 in FIGS. 1A and 1B will now be describedwith reference to FIG. 2 which represents the progression of theamplitude of the electromotive force V at the terminals of the secondarywinding 103 of the sensor according to the angular position θ of thetarget 111 with respect to the transducer 110.

In operation, the flow of an alternating current I_(P) is applied byelectrical means in the primary winding 101. The flow of the currentI_(P) in the winding 101 produces an electromagnetic field B having, inthe absence of a target, a substantially symmetrical distribution byrevolution in the circular annular strip traversed by the secondarywinding 103. By way of non-restrictive example, the frequency of thealternative excitation current I_(P) applied in the primary winding isbetween 500 kHz and 50 MHz (for example 4 MHz). The amplitude of thecurrent I_(P) is for example between 0.1 mA and 100 mA (for example 2mA). In the absence of a target 111, or, more generally, when theconductive pattern 107 of the target does not cover the secondarywinding 103, the secondary winding 103 supplies between the ends thereofan alternating EMF V, having a frequency substantially equal to theexcitation frequency of the primary winding, and having an amplitude inprinciple different to zero. When the conductive pattern 107 of thetarget 111 covers all or part of the secondary winding 103, the spatialelectromagnetic field distribution in the vicinity of the turn 103varies according to the arrangement and the displacement of the surfaceportion of the conductive pattern 107 situated facing the turn 103. Afurther formulation consists of considering that, under the effect ofthe magnetic excitation generated by the flow of the current I_(P) inthe primary winding, eddy currents appear in the conductive pattern 107,inducing a modification of the spatial distribution of theelectromagnetic field according to the arrangement and the displacementof the surface portion of the pattern 107 situated facing the turn 103.These changes or variations of the spatial distribution of theelectromagnetic field according to the arrangement and the displacementof the surface portion of the pattern 107 situated facing the turn 103,are conveyed, by induction, by variations or changes in the amplitude Vof the voltage range at the terminals of the secondary winding,according to the arrangement and the displacement of the surface portionof the pattern 107 situated facing the turn 103.

It is considered by way of non-restrictive illustrative example that thetarget can move in rotation about the axis Z with respect to thetransducer, in a range of angular positions from θ=−α° to θ=α°. It isconsidered arbitrarily that the position θ=−α° corresponds to thearrangement represented in FIG. 1A, wherein the conductive pattern 107does not conceal the turn 103, but has, viewed from above, a radial edgeadjoined to a radial edge of the turn 103. As such, for the angularpositions θ ranging from −α° to 0°, the surface area of the portion ofthe conductive pattern 107 situated facing the turn 103 increases whenthe angular position θ increases, and, for the angular positions θranging from 0° to α°, the surface area of the portion of the conductivepattern 107 facing the turn 103 decreases when the angular position θincreases. Outside the range of angular positions ranging from θ=−α° toθ=α°, the surface area of the portion of the conductive pattern 107facing the turn of the secondary winding 103 is zero, and the positionand/or the displacement of the target 111 with respect to the transducercannot be measured.

The amplitude V of the range of the voltage measured at the terminals ofa secondary winding of an inductive displacement sensor is theoreticallyproportional to the area of the portion of surface area of theconductive pattern of the target situated facing the secondary winding.As such, as seen in FIG. 2, for the angular positions θ ranging from −α°to 0°, the signal V decreases when the angular position θ increases,changing from a high value V_(max) for θ=−α° to a low value V_(min) forθ=0°, and for the angular positions θ ranging from 0° to α°, the signalV increases when the angular position θ increases, changing from the lowvalue V_(min) for θ=0° to the high value V_(max) for θ=α°. The signal Vis thus theoretically a triangular signal varying linearly betweenV_(min) and V_(max) over the angular range ranging from −α° to α°. Itwill be seen hereinafter that, in practice, the signal V hasnon-linearity zones and consequently tends to have a sinusoidal shape.

As such, in the range of angular positions from θ=−α° to θ=0°, or in therange of angular positions from θ=0° to θ=α°, the measurement of theamplitude V of the range of the electromotive force at the terminals ofthe secondary winding 103 makes it possible to determine the angularposition θ of the target with respect to the transducer. Although thevalue of the signal V varies according to the angular position θ of thetarget in the two angular position ranges mentioned above, themeasurement of the signal V does not make it possible to discriminatethe position values of the range from −α° to 0° from the position valuesof the range from 0° to α° (non-surjective measurement). The extent ofthe range of angular positions that could actually be measured by thesensor 100 is thus approximately equal to α°, provided that the angle αdoes not exceed 180°.

FIGS. 3A and 3B are front views schematically representing a furtherexample of an inductive angular position sensor having a general diskshape. This sensor comprises a transducer 112 represented in FIG. 3A anda target 114 represented in FIG. 3B. The target 114 in FIG. 3B differsfrom the target 111 in FIG. 1A essentially by the conductive patternthereof. In particular, the target 114 in FIG. 3B differs from thetarget 111 in FIG. 1A in that it no longer comprises a single conductivepattern 107, but a set of N conductive patterns 117 _(i) rigidlyconnected to the target, and suitable for moving with respect to thetransducer, N being an integer greater than or equal to 2 and i being aninteger ranging from 1 to N. The transducer 112 in FIG. 3A differs fromthe transducer 110 in FIG. 1A essentially by the shape of the secondarywinding 113 thereof. In particular, the secondary winding 113 of thetransducer 112 in FIG. 3A no longer comprises a single conductive turn,but a set of N turns 113 _(i). The target 114 in FIG. 3B is intended tobe rotatably mounted with respect to the transducer 112 in FIG. 3A,similarly or identically to that described with reference to FIGS. 1Aand 1B.

In this example, in a front view, the set of conductive patterns 117_(i) and the set of turns 113 _(i), consist of the repetition byrevolution of N substantially identical patterns, respectively 117 _(i)and 113 _(i). The repetition by revolution of these patterns isperformed with a spatial frequency of 2α, i.e. each pattern having anangular aperture substantially equal to α° is spaced from the closestneighbor thereof by a portion of empty circular annular strip ofortho-radial range substantially equal to α°.

For sensors wherein the general shape is a closed circular annularstrip, i.e. having an angular aperture equal to 360°, the value of theangular aperture α of the patterns is chosen preferably such thatα=360°/2N, in order to ensure a whole number of pattern repetitions perrevolution (over 360°). In the example in FIGS. 3A and 3B, N=6 andα=30°.

In other words, the transducer in FIG. 3A comprises a secondary winding113 comprising N loops or turns 113 _(i) in series. Each turn 113 _(i)has a shape of a circular band strip sector, of the same type as theturn 103 in FIG. 1A, and has an angular dimension approximately equal toα=360°/2N (i.e. α=30° in this example). The N turns 113 i are regularlydistributed along the 360° of the circular annular strip approximatelydefined by the turns 101 a and 101 b of the primary winding 101, i.e.two consecutive turns 113 _(i) of the secondary winding are separated byan annular strip portion having an angle approximately equal to α.

The target in FIG. 3B comprises N conductive patterns 117 _(i). Eachpattern 117 _(i) has a shape of a circular band strip sector, of thesame type as the conductive pattern 107 in FIG. 1, and has an angulardimension approximately equal to α=360°/2N. The N conductive patterns117 i are regularly distributed along an annular strip of the targetintended to be positioned facing the annular strip of the transducercontaining the turns 113 i.

Hereinafter in the present application, the term multi-pole sensor shallrefer to the sensors of the type described with reference to FIGS. 3Aand 3B, N denoting the number of poles of the sensor. In the example inFIG. 1A, if α adopts the value 180°, reference is made to a sensor withone pole pair. More particularly, the term multi-pole sensor shalldenote a sensor wherein an elementary conductive pattern is regularlyrepeated at least twice on the target along a parallel direction with adegree of freedom of displacement of the target with respect to thetransducer (i.e. along an ortho-radial direction in an angular sensor ofthe type described above).

By analogy with the electrical period of an electric motor with aplurality of pole pair, reference shall now be made to the angularaperture between two adjacent patterns 117 _(i), and to the angularaperture between two adjacent patterns 113 _(i), as being the electricalperiod of the sensor. In the specific case of the sensor in FIGS. 3A and3B, for which the conductive patterns have an angular aperture α° andthe hollows between these patterns also have an angular aperture α°, theelectrical period is equal to 2α°, and, conversely, the angular apertureof a conductive pattern is equal to an electrical half-period of thesensor, which is a preferred but not exclusive case. By design, forsensors wherein the general shape is a closed circular annular strip, anelectrical period is preferably a sub-multiple of 360°, since α=360°/2N.Under these terms, a multi-pole inductive sensor has a measurement rangeof α°, equal to half the electrical period thereof of 2α°. In theexample in FIG. 1A, if α adopts the value 180°, the electrical period isequal to 360°, and the measurement range is approximately equal to halfthe electrical period, i.e. 180°. In the example in FIGS. 3A and 3B forwhich α=30°, the electrical period is 2α=60°, and the measurement rangeis approximately equal to half the electrical period i.e. α=30°.

FIG. 4 is a diagram representing the progression of the amplitude V ofthe range of the electromotive force at the terminals of the secondarywinding 113 of the sensor in FIGS. 3A and 3B according to the angularposition θ of the target with respect to the transducer.

As seen in FIG. 4, when the angular position θ of the target withrespect to the transducer varies from 0° to 360°, the signal V variesperiodically between a high value V_(max) and a low value V_(min), withan angular period of variation approximately equal to the electricalperiod 2α of the sensor.

The amplitude of the range of angular positions θ suitable for beingmeasured by the sensor in FIGS. 3A and 3B is approximately equal to halfof the electrical period, i.e. α°.

One advantage of the sensor in FIGS. 3A and 3B with respect to thesensor in FIGS. 1A and 1B is that the greater number of patternsdistributed on the target and on the transducer enables a distributedmeasurement on an extended measurement zone, wherein each patterncontributes locally and by design to the generation of an overallelectromotive force, this electromotive force being more immune topositioning errors of the target with respect to the transducer than inthe sensor in FIGS. 1A and 1B, wherein the measurement made is a localmeasurement made using a single set of patterns 107-103. This robustnessof the measurement is especially great as the number N of pairs of polesof the sensor increases.

FIG. 5 illustrates an alternative embodiment of the sensor in FIGS. 3Aand 3B. In FIG. 5, only the transducer of the sensor has been shown, thetarget being identical to that in FIG. 3B.

The transducer of the sensor in FIG. 5 comprises the same elements asthe transducer in FIG. 3A, and further comprises a second secondarywinding 113′ comprising N loops or turns 113 _(i)′ in series. For thepurposes of clarity, the connections between the different loops 113_(i) of the winding 113 and the connections between the different loops113 _(i)′ of the winding 113′ have not been shown in FIG. 5. Thesecondary winding 113′ (represented as a dashed line) is substantiallyidentical to the secondary winding 113 (represented as a solid line),and is arranged in the same annular strip of the transducer as thesecondary winding 113, with an angular offset corresponding to a quarterof the electrical period of the sensor, i.e. approximately equal to α/2,with respect to the secondary winding 113.

FIG. 6 is a diagram representing the progression of the amplitude V (asa solid line) of the range of the electromotive force at the terminalsof the secondary winding 113 of the sensor in FIG. 5, and theprogression of the amplitude V′ (as a dashed line) of the range of theelectromotive force at the terminals of the secondary winding 113′ ofthe sensor in FIG. 5, according to the angular position θ of the targetwith respect to the transducer.

As seen in FIG. 6, when the angular position θ of the target withrespect to the transducers varies from 0° to 360°, the signals V and V′vary periodically between a high value V_(max) and a low value V_(min),with a variation period equal to the electrical period of the sensor,i.e. approximately equal to 2α° in this example, and with an angularoffset with respect to one another substantially equal to one quarter ofthe electrical period of the sensor, i.e. approximately α/2° in thisexample.

One advantage of the transducer in FIG. 5 with respect to the transducerin FIG. 3A is that it makes it possible to extend the range of angularpositions θ suitable for being measured by the sensors up toapproximately an entire electrical period (i.e.) 2α°), instead of ahalf-period (i.e. α°) in the example in FIGS. 3A and 3B.

FIG. 7 illustrates a further alternative embodiment of the sensor inFIGS. 3A and 3B. In FIG. 7, only the transducer of the sensor has beenshown, the target being identical to that in FIG. 3B.

The transducer of the sensor in FIG. 7 differs from the transducer inFIG. 3A essentially by the shape of the secondary winding thereof. Thetransducer of the sensor in FIG. 7 comprises a secondary winding 123comprising 2N loops or turns of alternating winding directions,interconnected in series. In other words, the secondary winding 123comprises 2N patterns of electrical circuits or turns, each beingconnected to the closest neighbor thereof in anti-series. Moreparticularly, the winding 123 comprises N turns 123 _(i+) of the samewinding direction, substantially identical to the N turns 113 _(i) ofthe transducer in FIG. 3A, and further comprises N turns 123 _(i−) ofopposite winding direction, each turn 123 _(i−) being arranged betweentwo consecutive turns 123 _(i+), and each turn 123 _(i−) having a shapeof a circular annular strip sector, of the same type as the turns 123_(i+). For the purposes of clarity, the connections between the turns123 _(i+) and 123 _(i−) of the winding 123 have not been shown in FIG.7, and the two winding directions have been represented schematically bya + sign for the turns 123 _(i+) and by a − sign for the turns 123_(i−).

More specifically, in the example in FIG. 7, the angular aperture α ofeach turn 123 _(i+) and 123 _(i−) has been chosen strictly less than anelectrical half-period so as to enable a more legible graphicrepresentation. In practice, the angular aperture α of each turn 123_(i+) and 123 _(i−) can approximate an electrical half-period with alower value, with an exact value, or with a greater value. In thespecific case where the angular aperture equals exactly one electricalhalf-period, which is a preferred but non-exclusive example of anembodiment, the sum of the angular apertures of the N turns 123 _(i+)and of the angular apertures of the N turns 123 _(i−) equals 360°, or inother words, the constituent radial tracks of two adjacent turns 123_(i+) and 123 _(i−) share the same spatial coordinates in a referenceframe {R, θ} (not shown) directed by the axis Z and having as a centerthe center of the sensor. This obviously does not mean however thatthese tracks are merged and that the turns 123 _(i+) and 123 _(i−) areshort-circuited, insofar as the tracks can be positioned on two separateplanes along the axis Z.

The spatial repetition period between two adjacent turns 123 _(i+), andthe spatial repetition period between two adjacent turns 123 _(i−), arekept equal to one electrical period of the sensor regardless of theangular aperture α of the turns 123 _(i+) and 123 _(i−). A preferred butnon-restrictive example of use of such a set of turns having an angularaperture different from an electrical half-period of the sensor consistsof distributing the turns 123 _(i+) and 123 _(i−) regularlyortho-radially as illustrated in FIG. 7.

FIG. 8 is a diagram representing the progression of the amplitude V ofthe range of the electromotive force at the terminals of the secondarywinding 123 of the sensor in FIG. 7 according to the angular position θof the target with respect to the transducer.

As seen in FIG. 8, when the angular position θ of the target withrespect to the transducer varies from 0° to 360°, the signal V variesperiodically between a high value V_(max) and a low value V_(min), withan angular period of variation approximately equal to one electricalperiod.

One advantage of the transducer in FIG. 7 with respect to the transducerin FIG. 3A is that the amplitude V is approximately centered around 0volts (V_(min)≈−V_(max)). More generally, the use of a spatiallydifferential measurement, such as that which is for example describedwith reference to FIG. 7, makes it possible to a low mean amplitude Vwith respect to the values V_(min) et V_(max). This simplifies theprocessing of the measurement for the purposes of estimating thedisplacement, and in particular reduces the influence of drift andparasitic disturbances.

Indeed, some variations of the amplitude V associated with parasiticeffects, i.e. not originating from the displacement of the target, aremerely conveyed by a gain variation in the case of the sensor in FIG. 7,whereas they are conveyed both by a gain variation and an offsetvariation in the case of the sensor in FIG. 3A. This is for example thecase when the coupling coefficient between the primary, the target andthe secondary varies due to a parasitic variation of thetarget-transducer distance. This is furthermore the case when theamplitude of the excitation current varies, for example in the case ofparasitic fluctuation of the power supply voltage, or in the event ofdrift of the electrical properties of the primary winding, for exampleaccording to the temperature and the relative distance of the transducerand the target.

Moreover, in the example in FIG. 7, the coupling of the secondarywinding with external fields not carrying information on thedisplacement of the target, is considerably reduced due to the spatiallydifferential nature of the measurement. This is particular the case forthe portion of the electromagnetic field generated by the primary whichinduces the constant portion (independent of the target position) of theamplitude of the EMF, but also for any external electromagneticinterference exhibiting a substantially uniform distribution in thevicinity of the secondary winding 123.

The alternative embodiment in FIG. 7 can be combined with thealternative embodiment in FIG. 5 in order to obtain two signals ofamplitude V and V′ angularly offset by a quarter of an electrical periodand centered on approximately 0 volts.

It should be noted that the fact that the amplitude V of the range ofthe EMF is approximately centered on 0 volts does not necessarily meanthat the modulated electromotive force verifies said properties beforethe implementation of a method of frequency transposition and filtering.Generally, the electromotive force (modulated) has a mean valuedifferent to zero, either due to voluntary referencing of one of the twoterminals of the secondary winding at a defined electric potential(electrical mass for example), or due to referencing by capacitivecoupling of the mean potential thereof to the potential of theenvironment (for example the mechanical mass) in the case of ahigh-impedance measurement at the secondary winding. This illustrativeexample applied to the mean value of the electromotive force is alsoapplicable to any frequency component of the electrical signal,regardless of the origin thereof, which is situated outside a frequencyband of interest −Δf to +Δf about the modulation frequency, or, in otherwords, which is situated outside a frequency band of interest −Δf to +Δfabout the zero frequency following the frequency transposition method.

First Aspect

FIG. 9A is a diagram representing the expected theoretical progressionof the signals of amplitude V and V′ according to the angular positionθ, in an inductive sensor of the type described above combining theembodiment options in FIGS. 5 (two secondaries spatially offset by onequarter of an electrical period) and 7 (each secondary comprises 2Nturns of alternating winding directions). As seen in FIG. 9A, theexpected theoretical amplitudes V and V′ are triangular periodic signalshaving a period equal to the electrical period of the sensor, varyinglinearly between the values V_(min) and V_(max), with an angular offsetof one quarter of an electrical period with respect to one another.Indeed, in theory, as indicated in the patent EP0182085 mentioned above(column 12, lines 22 to 57), the amplitude of the range of the voltagemeasured at the terminals of secondary winding of an inductive sensor isproportional to the area of the portion of surface of conductivepatterns of the target situated facing this secondary winding. However,in the examples of embodiments described above, the portion ofconductive surface of the target situated facing the electrical circuitpatterns or turns of the secondary winding varies linearly with theangular position θ, for the patterns 123 _(i+) and for the patterns 123_(i−) in FIG. 7. Therefore, the signals V and V′ should vary linearly byportions according to the position θ.

The inventors observed, however, that in practice the variation of thesignals V and V′ according to the position θ generally has widenon-linear zones in an electrical period of the sensor. Morespecifically, in practice, the variation of the signals V and V′according to the position θ indeed has two substantially linear zones ofreduced range in an electrical period of the sensor, these zones beingapproximately centered on the zero crossings of the amplitudes V and V′,but, between these linear zones, saturated and de facto less linearzones are inserted, these zones being approximately centered on extremaof the amplitudes V and V′.

The low linearity of the amplitudes V and V′ according to the position θinvolves drawbacks. In particular, by way of non-restrictive example,having ranges of reduced linearity does not make it possible to benefitfully from the signal processing methods described in the patentsFR2914126 and FR2891362.

FIG. 9B is a diagram representing the actual progression, typicallyobtained in practice, of the signals V and V′ according to the angularposition θ in an inductive sensor of the type described above. As seenin FIG. 9B, the signals V and V′ only vary linearly in portions ofreduced angular range α_(L) of the measurement range of the sensor,referred to as linearity ranges. By way of example, each linearity rangeα_(L) has a range between 20% and 90% of the electrical half-period ofthe sensor (equal to α° in the example shown). The linearity range α_(L)is for example defined as being the maximum angular range, substantiallycentered on the mean value of the amplitude V, for which it is possibleto find a linear approximation V_(L) to the amplitude V, such that thedifference E_(L) between the linear approximation V_(L) and theamplitude V is less than a threshold E_(L0), the threshold E_(L0) beingfor example defined as a percentage of the extrema of the amplitude V,for example in a range of values between 0.01% and 10% of the extrema ofthe amplitude V according to the degree of linearity sought for thesensor. In other words, the linearity range α_(L) is the maximum angularrange whereon the amplitude V varies substantially linearly with theposition of the target with respect to the transducer, within onemaximum approximation of set value E_(L0). In practice, it is generallysought to do the opposite, i.e. evaluate the maximum linearity errorE_(LM) over a given angular range α_(L), for example but notrestrictively the angular range whereon it is sought to make themeasurement. Also, a further manner to assess the linearity of a sensoris that of assessing the linearity error E_(LM), defined as the maximumdifference between the amplitude V and the linear approximation V_(L)for a given range α_(L). Preferably but not restrictively, the linearityrange sought for a sensor with two secondary windings is at least 50% ofan electrical half-period, for example between 50% and 80% of anelectrical half-period when the displacements to be measured are rapidand the observation of a plurality of samples of the amplitude requiresgoing beyond 50% of an electrical half-period. In a further preferredexample, the linearity range sought for a sensor with three secondarywindings is at least 33% of an electrical half-period, for examplebetween 33% and 50% of an electrical half-period when the displacementsto be measured are rapid. Hereinafter, unless specified otherwise andwithout being considered to be an exclusive choice, the description willbe limited to presenting a sensor with two secondary windings, and thepurposes of legibility, the description will be limited to presentingthe linearity error over a sought linearity range of 50% of anelectrical half-period, without explicitly mentioning these terms, andreferring to the linearity error defined under these terms by merelymentioning the linearity error E_(L).

The inventors particularly observed that, for a given target-transducerdistance (and for a given range α_(L)), the linearity error E_(L)generally increases as the number N of poles of the sensor increases.

However, this restriction does not indicate industrial use of aninductive sensor insofar as such a use generally requires a high numberof poles, typically N=6, to ensure a robust measurement as stated above.

It would be desirable to be able to have inductive displacement sensors,and particularly multi-pole sensors, having a lower linearity error (orbroader linearity ranges) than existing sensors, in order in particularto facilitate the processing of the amplitudes supplied by the sensor.By way of non-restrictive example, extending the linearity ranges canmake it possible to benefit from the signal processing methods describedin the patents FR2914126 and FR2891362.

According to a first aspect, it is sought, in an inductive displacementsensor, and particularly (but not only) a multi-pole sensor, for examplesensor with two pole pairs or more and preferably a sensor with six polepairs or more, to reduce the linearity error E_(L) over a given angularrange α_(L), for example over a range α_(L) extending over half anelectrical half-period of the sensor for a sensor with two secondarywindings, or over a range α_(L) extending over one third of anelectrical half-period for a sensor with three secondary windings. Itcan also be taken into consideration that it is sought to increase theextent of the linearity range of the sensor, i.e. the extent of theposition range, included in the measurement range of the sensor, whereinthe amplitude of the range of the electromotive force at the terminalsof a secondary winding of the sensor varies approximately linearlyaccording to the angular position θ of the target with respect to thetransducer.

The studies conducted by the inventors demonstrated that the extents ofthe linearity range of an inductive sensor is dependent on thetarget-transducer distance d, sometimes referred to as air gap, i.e. thedistance between the median plane of the secondary winding(s) of thetransducer, and the conductive patterns of the target. By way ofexample, the target-transducer distance d is defined as being thedistance between the median plane of the secondary winding(s) of thetransducer and the surface of the conductive patterns of the targetoriented towards the transducer.

FIG. 10 is a diagram representing, for a plurality of separatetarget-transducer distances in an inductive sensor of the type describedabove (for example of the type described with reference to FIG. 7, whereN=6 pole pairs), the progression of the amplitude V of the range of theelectromotive force measured at the terminals of a secondary winding ofthe transducer according to the angular position θ of the target. Thecurve V1 represents the progression of the amplitude V for atarget-transducer distance d1, the curve V2 represents the progressionof the amplitude V for a target-transducer distance d2 less than d1, andthe curve V3 represents the progression of the amplitude V for atarget-transducer distance d3 less than d2. The line V11, in dotted-lineformat, represents the linear approximation of the amplitude V1, theline V12, in dotted-line format, represents the linear approximation ofthe amplitude V2, and the line V13, in dotted-line format, representsthe linear approximation of the amplitude V3. As seen in FIG. 10, thesignal V has, at the distance d3, a maximum amplitude greater than themaximum amplitude obtained at the distances d2 and d1. On the otherhand, the linearity error E_(L2) of the amplitude V, at the distance d2,is less than the linearity errors E_(L1) and E_(L3) of the amplitude Vat the distances d1 and d3 respectively.

FIG. 11 is a diagram representing the progression, according to thetarget-transducer distance, of the linearity error E_(L) of theamplitude V of the range of the electromotive force measured at theterminals of a secondary winding of the transducer of an inductivedisplacement sensor, for example a sensor of the type described withreference to FIG. 7 (where N=6 pole pairs). In this example, thelinearity error E_(L) corresponds, in a given range of angular positionsθ extending for example over half of the electrical period of the sensor(over a monotone portion of the EMF), at the maximum difference (inabsolute value) between a linear approximation of the response of thesensor and the actual response measured. As seen in FIG. 11, there is anoptimal target-transducer distance d_(opt) for which the linearity errorE_(L) passes through a minimum. More generally, the inventors observedthat a minimum linearity error can be observed in all the types ofinductive displacement sensor, regardless of the number of pole pairs inparticular. This minimum value is achieved for an optimaltarget-transducer distance which is dependent on the configuration ofthe sensor (and particularly on the number of pole pairs). It is thustheoretically possible to obtain a linear response regardless of theinductive sensor. The term theoretically denotes that, when the numberof pole pairs N is particularly high, the distance d_(opt) becomesextremely small so as no longer to be measurable in practice during thelimited precision and constraints of use of suitable measuringinstruments.

According to a first embodiment, an inductive displacement sensor isenvisaged wherein the target-transducer distance d is between 0.8 and1.5 times the distance d_(opt) for which the linearity error of theamplitude measured by the sensor is minimal. It should be noted thatthis optimal distance can easily be determined using tests, for exampleby plotting curves of the type represented in FIG. 11.

The inventors observed however that, in practice, for some sensors, andparticularly sensors having a high number N of pole pairs, typicallygreater than or equal to three and more particularly for N greater thanor equal to six, the optimal target-transducer distance in terms oflinearity can be relatively small, for example less than 0.2 mm, whichcan pose problems for some types of measurement, particularly inindustrial environments wherein such distances are unacceptable,particularly due to manufacturing, assembly and use tolerances.

Moreover, the inventors observed that the optimal target-transducerdistance in terms of linearity is dependent on a plurality of furtherparameters, including geometric parameters of the sensor such as theouter diameter of the transducer and/or the target. More particularly,the inventors observed that when the diameter of the sensors increases,the optimal target-transducer distance increases and can adopt arelatively high value, for example greater than 1 mm, which can poseproblems for some types of measurements, particularly in industrialenvironments wherein it is sought to ensure a somewhat compact design.

In the case where the optimal target-transducer distance in terms oflinearity is incompatible (excessively high or excessively low) with themeasurement environment, it is possible to envisage positioning at theclosest possible target-transducer distance to the optimal distance inthe environmental constraint limits, and correcting the non-linearity byapplying mathematical processing (post-processing) of the measurementsignal. The inventors observed however that, in practice, this solutionhas limitations in terms of precision and robustness, and is notsatisfactory particularly for the implementation of the signalprocessing methods described in the patents FR2914126 and FR2891362.

A first solution proposed by the inventors and illustrated by FIGS. 12Ato 12D, 13A to 13C, 14 and 15, is that of adding to the sensor anadditional electromagnetic field confinement part, placed at a specificdistance from the primary winding of the transducer, chosen so as toincrease the target-transducer distance significantly in terms oflinearity.

FIGS. 12A to 12D are cross-sectional views schematically illustratingfour examples of embodiments of an inductive angular displacementsensor.

In the example in FIG. 12A, the sensor comprises a transducer 201 and atarget 203, arranged at a target-transducer distance d (d being in thisexample the distance between the median plane of the secondarywinding(s) of the transducer and the plane of the surface of theconductive patterns of the target oriented towards the transducer), anddoes not comprise an additional field confinement part.

In the example in FIG. 12B, the sensor comprises a transducer 201 and atarget 203, arranged at a target-transducer distance d, and furthercomprises an additional field confinement part 205 made of a conductivematerial, for example made of the same material as the conductivepatterns of the target, or of any other conductive material, optionallymagnetic, such as iron, steel, aluminum, copper, etc. In this example,the part 205 is arranged on the side of the target 203 opposite thetransducer 201 (i.e. the target 203 is situated between the transducer201 and the part 205), the surface of the part 205 oriented towards thetarget 203 being preferably approximately parallel with the median planeof the transducer, and therefore also approximately parallel with themedian plane of the target (subject to assembly imprecision). The fieldconfinement part 205 is preferably periodic along a parallel directionwith a degree of freedom of displacement of the sensor, i.e. periodic byrevolution (about an axis which is approximately the axis of symmetry ofthe target) in the case of an angular position sensor, the spatialperiod of the conductive patterns of the confinement part beingpreferably separate from that of the conductive patterns of the target.By way of illustrative but non-restrictive example, the part 205 issymmetric by revolution. The part 205 is arranged at a part-transducerdistance l, defined in this example as being the distance between themedian plane of the primary winding(s) of the transducer, and the planeof the surface of the conductive pattern(s) of the part oriented towardsthe transducer. The part 205 is preferably rigidly connected to thetarget, i.e. movable with respect to the transducer when the position ofthe target with respect to the transducer changes.

In the example in FIG. 12C, the sensor comprises a transducer 201 and atarget 203, arranged at a target-transducer distance d, and furthercomprises an additional field confinement part 205′, for exampleidentical or similar to the part 205 in FIG. 12B. The part 205′ ispreferably periodic by revolution, and for example symmetric byrevolution, about an axis of symmetry which is approximately the axis ofsymmetry of the primary winding of the transducer. In this example, thepart 205′ is placed on the side of the transducer 201 opposite thetarget 203 (i.e. the transducer 201 is situated between the target 203and the part 205′). The part 205′ is arranged at a part-transducerdistance l′. By way of example, the distance l′ is defined as being thedistance between the median plane of the primary winding(s) of thetransducer, and the plane of the surface of the conductive patterns ofthe part oriented towards the transducer. The part 205′ is preferablyrigidly connected to the transducer, i.e. fixed with respect to thetransducer when the position of the target with respect to thetransducer changes.

In the example in FIG. 12D, the sensor comprises a transducer 201 and atarget 203, arranged at a target-transducer distance d, a first fieldconfinement part 205 (for example identical or similar to the part 205in FIG. 12B) arranged on the side of the transducer 201 opposite thetarget 203, at a distance l from the transducer, and a second fieldconfinement part 205′ (for example identical or similar to the part 205′in FIG. 12C), arranged on the side of the target 203 opposite thetransducer 201, at a distance l′ from the transducer (i.e. thetransducer 201 and the target 203 are situated between the parts 205 and205′).

The parts 205 and/or 205′ can be electrically connected or not,point-wise or in a spatially distributed manner, to other elements ofthe sensor. In particular, the part 205 can be electrically connected toone or a plurality of conductive patterns of the target, and the part205′ can be electrically connected to an electrical potential availableon the transducer, for example at a point of a secondary winding, at apoint of the primary winding, or to the ground of the transducer.

FIG. 13A is a diagram including four curves E_(LA), E_(LB), E_(LC) andE_(LD) representing respectively, for the four examples of a sensor inFIGS. 12A to 12D, the progression of the linearity error E_(L) of thesensor according to the target-transducer distance. Each of the curvesE_(LA), E_(LB), E_(LC) and E_(LD) is of the same type as the curve inFIG. 11, i.e. it passes via a linearity error value for a certainoptimal target-transducer distance, d_(optA), d_(optB), d_(optC) andd_(optD), respectively. As seen in FIG. 13A, the distance d_(optA) isless than the distance d_(optB) which is in turn less than the distanced_(optC) which is in turn less than the distance d_(optD). The testsconducted by the inventors demonstrated that adding one or a pluralityof additional field confinement parts can increase the optimaltarget-transducer distance in terms of linearity of an inductivedisplacement sensor from several tens of millimeters to severalmillimeters.

The positioning along the axis Z of the additional field confinementpart(s), and more specifically the distance between this or these partsand the primary winding of the transducer, has an influence on theeffectiveness of the increase in the optimal target-transducer distancein terms of linearity resulting from adding this or these parts. Thereis therefore a (some) optimal distance(s) l_(opt) and/or l_(opt)′between the primary winding and the additional field confinementpart(s), such that the optimal target-transducer distance d_(opt) isincreased to attain a value between 0.65 and 1.25 times the distance dat which it is sought to have the sensor operate, this sought valuepossibly being but not restrictively between 0.5 and 1.5 mm, which is arange of values compatible with various industrial applications.

FIG. 13B is a diagram representing the progression, for an inductiveangular displacement sensor of the type described above, of the optimaltarget-transducer distance d_(opt) in terms of linearity, according tothe ratio of the part-primary distance d_(pipr′) over the target-primarydistance d_(cpr), in the case of addition of the additional fieldconfinement part 205′ as represented in FIG. 12C or 12D. As seen in FIG.13B, the optimal target-transducer distance in terms of linearityincreases as the ratio d_(pipr′)/d_(cpr) decreases.

FIG. 13C is a diagram representing the progression, for an inductiveangular displacement sensor of the type described above, of the optimaltarget-transducer distance d_(opt) in terms of linearity, according tothe ratio of the part-primary distance d_(pipr) over the target-primarydistance d_(cpr), in the case of addition of the additional fieldconfinement part 205 as represented in FIG. 12B or 12D. As seen in FIG.13C, the optimal target-transducer distance in terms of linearityincreases as the ratio d_(pipr′)/d_(cpr) decreases.

In other words, if the transducer is considered as an assembly whereinthe constituent layers are not differentiated, the optimaltarget-transducer distance d_(opt) can be said to increase as the ratiol/d (respectively l′/d) decreases.

Under these conditions, an illustrative but non-restrictive example ofpositioning of the additional field confinement parts in FIG. 12D, isthat of placing:

-   -   the upper part 205′ at a distance from the primary winding        approximately between 0.5 and 2 times the distance separating        the primary winding and the surface area of the conductive        patterns of the target;    -   the lower part 205 at a distance from the primary winding        approximately between 1.3 and 3 times the distance separating        the primary winding and the surface area of the conductive        patterns of the target.

As such, for a given sensor configuration, the ratio d_(pipr)/d_(cpr)and/or the ratio d_(pipr′)/d_(cpr) can be chosen such that the distanced_(opt) is compatible with the constraints of the application, forexample either greater than or equal to 0.3 mm, for example between 0.3and 10 mm, and preferably between 0.5 and 1.5 mm, particularly for asensor including a high number N of pole pairs, for example N≥4 andpreferably N≥6.

It should be noted that the abovementioned choice of distance betweenthe field confinement part and the transducer is generally not optimalin terms of signal level supplied by the secondary winding(s) of thetransducer. Indeed, at this distance, the conductive part 205/205′causes a non-negligible reduction in the level of the signals V and V′supplied by the transducer. It should be noted in particular that in theprior art of inductive angular displacement measurement, it is acceptedto separate the conductive parts liable to modify the spatialdistribution of the electromagnetic field which is established in thepresence of only the primary, secondary and target elements as much aspossible. This dimensioning criterion applies in particular in the caseof electrostatic screens (or shielding screens), which, when provided,are arranged at distances along the axis Z much greater than thedistances envisaged in the embodiments described, so as not to attenuatethe wanted signal level measured at the secondary excessively.

However, the embodiments proposed define a compromise which may beappropriate in applications for which the linearity is important, andparticularly in applications wherein it is sought to implement signalprocessing methods of the type described in the patents FR2914126 andFR2891362 mentioned above.

FIGS. 14 and 15 are front views representing examples of fieldconfinement parts 205 liable to be used in an inductive displacementsensor of the type described above (the parts 205′ of the sensorsmentioned above can have similar or identical configurations). In theexample in FIG. 14, the part 205 is a mere disk made of a conductivematerial (for example metal) having a diameter for example greater thanor equal to the outer diameter of the target. Alternatively (not shown),the disk can be drilled at the center thereof, for example with a holeless than or equal to the inner diameters of the conductive patterns ofthe target. In the example in FIG. 15, the part 205 is a disk of thesame diameter but having cohesive radial striations or slots with thepatterns of the target, suitable for obtaining a Moiré type structureeffect with the target suitable for amplifying the influence of the part205 on the field distribution at a secondary winding of the transducer.The embodiments described are, however, not restricted to these twoparticular examples.

A second solution for modifying the optimal target-transducer distancein terms of linearity, suitable for use in addition or as an alternativeto adding a conductive field confinement part, is illustrated by FIGS.16A, 16B and 17.

FIGS. 16A and 16B illustrate two examples of embodiments of an inductiveangular position sensor. In FIGS. 16A and 16B, only the target of thesensor has been represented. The arrangement of the transducer, andparticularly of the primary winding thereof or the secondary windingsthereof, is consistent with the arrangement of the target, and caneasily be deduced from the shape of the target on reading the above. Inthis example, the target of the sensor in FIG. 16A is similar oridentical to the target in FIG. 3B. The target of the sensor in FIG. 16Balso comprises N conductive patterns 137 _(i) in the shape of an annularstrip sector of angular aperture α approximately equal to one electricalhalf-period (for example 360°/2N), the N patterns 137 _(i) beingregularly distributed along an annular strip described by the target.The target in FIG. 16B differs from the target in FIG. 16A in that theconductive patterns 137 _(i) have different radial dimensions (less inthe example shown) from the radial dimensions of the conductive patterns117 _(i) of the target in FIG. 16A. More particularly, in this example,the annular strip determining the shape of the conductive patterns 137_(i) has an external radius R_(ext) substantially identical to that ofthe annular strip determining the shape of the patterns 117 _(i), buthas an internal radius R_(int) less than that of the annular strip ofthe conductive patterns 117 _(i).

The inventors observed, as illustrated by FIG. 17, that, for a givennumber of pole pairs, the optimal target-transducer distance d_(opt) interms of linearity of the response of the sensor, varies according tothe ratio R_(int)/R_(ext) between the internal radius and the externalradius of the annular strip wherein the conductive patterns of thetarget are situated, and consequently wherein the turns of the secondarywinding(s) of the sensor are situated. It should be noted that theembodiment of FIG. 16B, which consists of varying the ratioR_(int)/R_(ext) by modifying the internal radius R_(int) of theconductive patterns of the target, is in no way exclusive of furtherembodiments suitable for varying the ratio R_(int)/R_(ext) by modifyingeither the external radius R_(ext), or both radii in combination.

FIG. 17 is a diagram representing the progression, for an inductiveangular displacement sensor of the type described above, of the optimaltarget-transducer distance d_(opt) in terms of linearity, according tothe ratio R_(int)/R_(ext). As seen in FIG. 17, the optimaltarget-transducer in terms of linearity increases as the ratioR_(int)/R_(ext) increases. As such, for a given sensor configuration,the ratio R_(int)/R_(ext) can be chosen such that the distance d_(opt)is compatible with the constraints of the application, for exampleeither greater than or equal to 0.3 mm, for example between 0.3 and 10mm, and preferably between 0.5 and 1.5 mm, particularly for a sensorincluding a high number N of pole pairs, for example N≥4 and preferablyN≥6.

In electromagnetic terms, it would appear that the modifications made tothe internal and/or external radii of the target have the effect ofmodifying the conductive pattern shape ratio, and in particularmodifying the contribution of the radial edges with respect to thecontribution of the ortho-radial edges, this ratio of the contributionsbeing a determining factor of the optimal target-transducer distance interms of linearity d_(opt). When the ratio R_(int)/R_(ext) between theinternal radius and the external radius of the target increases, theannular strip portion constituting a conductive pattern is compressedalong the radial direction, inducing a reduction in the contribution ofthe radial edges to the overall field distribution measured by thesecondary, conveyed at the secondary output signal by an increase in theoptimal target-transducer distance in terms of linearity. The solutiondescribed therefore consists of modifying the spatial distribution ofthe electromagnetic field, and more particularly the ratio of the radialcontributions with respect to the ortho-radial contributions, so as toadjust the optimal target-transducer distance in terms of linearityd_(opt) so that it is compatible with the constraints of theapplication.

In the sensor in FIG. 16B, when the internal radius R_(int) and/or theexternal radius R_(ext) of the target in FIG. 16B change, the internaland external radii of the associated transducer change preferablysubstantially in the same proportions, so as to maximize the signallevel received by the secondary. By maximizing the signal level at thesecondary output, reference is more specifically made to maximizing theslope at the origin of the signal rather than maximizing the valuesadopted by the signal extrema for some positions.

For a given set of internal R_(int) and external R_(ext) target radii,the signal received by the secondary of the associated transducer ismaximum when the annular strip defining the patterns of the target andthe annular strip defining the patterns of the secondary aresubstantially overlaid, or in other words, when the external andrespectively internal ortho-radial edges of the target and the externaland respectively internal ortho-radial branches of the secondary areoverlaid.

It should be noted that for a given sensor size (and particularly for anupper external radius limit and a lower internal radius limit),increasing the ratio R_(int)/R_(ext) amounts to decreasing the surfacearea of the conductive patterns of the target, which induces a decreasein the amplitude of the variations of the sensor output signal levelaccording to the position of the target with respect to the transducer.As such, in the prior art of inductive angular displacement measurement,the internal diameter and the external diameter of the annular stripwherein the conductive patterns of the target are situated, andconsequently wherein the turns of the secondary winding(s) of the sensorare situated, are designed so as to occupy the maximum surface areaavailable in the given size, the size being generally restricted by theinternal aperture and the external diameter of the substrate and/or thecasing wherein the sensor is integrated, or by the external diameter ofthe shaft about which the sensor is fitted and by the internal diameterof the interface parts between which the sensor is housed.

Nevertheless, the proposed solution consisting of modifying the ratioR_(int)/R_(ext) defines a compromise which may be appropriate inapplications for which linearity is important.

A third solution for modifying the optimal target-transducer distance interms of linearity, suitable for use in addition or as an alternative toadding an additional field confinement part, and/or to modifying theratio R_(int)/R_(ext), is illustrated by les FIGS. 18A, 18B and 19.

This third solution follows the same logic as the solution that has justbeen described, in that it consists of modifying the shape factor of theconductive patterns of the target and/or the corresponding secondarywinding turns, and particularly of modifying the ratio between theradial dimension and the ortho-radial dimension of the patterns of thetarget and/or secondary winding turns, so as to adapt the optimaltarget-transducer distance in terms of linearity to the constraints ofthe application.

FIG. 18A illustrates three examples of embodiments of an angularposition sensor of the type described above. In FIG. 18A, only oneconductive pattern of the target, designated respectively by thereferences 117 _(i) for the first example (solid line), 117 _(i)′ forthe second example (dashed line), and 117 _(i)″ for the third example(dotted line), has been shown. In each example, the target is obtainedby regularly repeating the conductive pattern represented along acircular annular strip. The internal and external radii of the patterns117 _(i), 117 _(i)′, and 117 _(i)″ are substantially identical, but thepatterns 117 _(i), 117 _(i)′, and 117 _(i)″ differ from one another bythe angular dimensions thereof. More particularly, in this example, theangular aperture of the pattern 117 _(i)′ is approximately equal to oneelectrical half-period (for example 360°/2N), as described above, theangular aperture of the pattern 117 _(i)″ is greater than one electricalhalf-period of a value Δα1, for example between 0% and 50% of anelectrical half-period, and the angular aperture of the pattern 117 _(i)is less than 360°/2N of a value Δα2, for example between 0% and 50% ofan electrical half-period.

As for the embodiment of the solution in FIGS. 16A, 16B and 17, thearrangement of the secondary of the transducer is preferentiallyconsistent with the arrangement of the conductive patterns of thetarget, i.e. the angular aperture of the secondary patterns adapted tothe patterns 117 _(i)′ of the target is substantially equal to oneelectrical half-period (for example 360°/2N), the angular aperture ofthe secondary patterns adapted to the patterns 117 _(i)″ of the targetis greater than 360°/2N of a value substantially equal to Δα1, and theangular aperture of the secondary patterns adapted to the target 117_(i) is less than 360°/2N of a value substantially equal to Δα2. Inpractice, when the angular aperture of the secondary patterns adopts avalue greater than an electrical half-period of the sensor, it can beenvisaged, in order to provide electrical insulation between adjacentturn tracks, to modify the shape of the tracks in at least onemetallization plane, and/or to increase the number of metallizationplanes. A further embodiment option can consist of limiting the maximumangular aperture of the patterns of the secondaries to substantially oneelectrical half-period, and only varying the angular aperture of thepatterns of the target (of the values Δα1 or Δα2). In this case, theangular aperture of the secondary winding patterns of the transducer isnot strictly consistent with the angular aperture of the patterns of thetarget.

The inventors observed that the optimal target-transducer distanced_(opt) in terms of linearity of the response of the sensor, variesaccording the angular deviation Δα between the angular aperture chosenfor the patterns of the target and the secondary, and the nominalangular aperture α equal to one electrical half-period of the sensor.

FIG. 19 is a diagram representing the progression, for a givenmulti-pole angular displacement sensor of the type described above andillustrated in FIGS. 18A and 18B, of the optimal target-transducerdistance d_(opt) in terms of linearity, according to the value Δα. Asseen in FIG. 19, the optimal target-transducer distance in terms oflinearity decreases as the value Δα increases for negative values, andconversely increases as the value Δα increases for positive values. Assuch, for a given sensor configuration, the angular aperture of theconductive patterns of the target can be modified by a value Δα withrespect to the nominal value α (equal to one electrical half-period, forexample 360°/2N), the value Δα being chosen such that the distanced_(opt) is compatible with the constraints of the application, forexample either greater than or equal to 0.3 mm, for example between 0.3and 10 mm, and preferably between 0.5 and 1.5 mm, particularly for asensor including a high number N of pole pairs, for example N≥4 andpreferably N≥6.

Solutions have been described for reducing the linearity error (orincreasing the extent of the linearity range) of the response of aninductive displacement sensor, as well as for modifying, i.e. increasingor reducing according the initial situation, the target-transducerdistance for which an inductive displacement sensor has or approachesoptimal characteristics in terms of linearity.

It should be noted that if the linearity error remains nonethelessexcessively high (or if the extent of the linearity range obtainedremains insufficient), one or a plurality of additional secondarywindings, spatially offset (by a substantially equal angular offsetbetween one another), may be added, so as to reduce the extent of theminimal linearity range required for proper reconstruction of theinformation in respect of positioning and/or displacement of the target,in combination with the application of the solutions described above. Byway of illustrative example, in the sensor in FIG. 5, instead ofproviding two identical secondary windings spatially offset by a quarterof an electrical period, it is possible to envisage three identicalsecondary winding spatially offset by a sixth of the electrical periodof the sensor.

Furthermore, it should be noted that the solutions described above canbe adapted to inductive linear displacement sensors, for example by“unwinding” the patterns in circular strip form described above in orderto convert same into patterns in rectilinear strip form.

Moreover, it should be noted that the solutions described above can beadapted to inductive angular displacement sensors wherein the transducerhas an angular aperture less than 360°, for example less than 180° inorder to enable assembly “from the side” of the transducer about arotary shaft, rather than a “through” assembly. In this case, theangular aperture of the target can have a value of 360°, independent ofthe angular aperture of the transducers, or adopt a value less than360°, corresponding for example to the angular displacement range of theapplication.

Second Aspect

The inventors further observed that, in practice, independently of theissue of linearity, existing inductive displacement sensors, andparticularly multi-pole sensors, are sensitive to various disturbancesinduced by coupling effect. Such disturbances occur for example at thetransduction zone, i.e. directly at the secondary of the transducer, andfurthermore at the electrical connection zone between the secondary ofthe transducer and a functional conditioning block of the electronicmeans. These disturbances particularly feature the coupling ofelectromagnetic disturbances from outside the sensor (i.e. not generatedby the primary winding), direct inductive coupling of the primarywinding with the secondary winding (i.e. the proportion of inductivecoupling remaining constant regardless of the position of the target),and/or capacitive coupling between the primary winding and the secondarywinding. These disturbances can cause undesirable fluctuations of thesensor output signal(s) and sensor output signal interpretation errors.

It would be desirable to be able to avail of inductive displacementsensors, and particularly multi-pole sensors, less sensitive toparasitic disturbances and/or less subject to parasitic couplings thanexisting sensors.

As such, according to a second aspect, it is sought to reduce thesensitivity to disturbances and parasitic coupling effects of multi-poleinductive displacement sensors, and more particularly of the sensors ofthe type described with reference to FIG. 7, i.e. wherein the secondarywinding(s) each comprise 2N turns of alternating winding directions, Nbeing the number of pole pairs of the sensor. For this, the inventorspropose a particular arrangement of the secondary winding(s) of thesensor, which will be described hereinafter.

FIGS. 20A and 20C schematically illustrate two examples of embodimentsof an inductive angular displacement sensor, of angular aperture 360°,consisting of N=6 pole pairs, and making a spatially differentialmeasurement (for example as described with reference to FIG. 7). InFIGS. 20A and 20C, only one secondary 213 of each sensor has been shown,the embodiment of the primary winding, the target, and, optionally, oneor a plurality of secondary windings spatially offset with respect tothe winding 213, being within the grasp of those skilled in the art onthe basis of the explanations of the present description. In thisexample, the secondary of the sensor in FIG. 20A and the secondary ofthe sensor in FIG. 20C are similar or identical to the secondary in FIG.7, except that the electrical connections between the turns are shown.The secondary in FIG. 20A shows a first method for interconnecting theturns, whereby the entire angular aperture of the annular strip whereonthe secondary extends is traversed a first time, for example in thetrigonometric direction in the figure, and the entire annular strip istraversed a second time, this time in the clockwise direction, so as toapproach the electrical terminal end E2 towards the electrical startingend E1, and thereby close the measurement circuit. The secondary in FIG.20C shows a second method for interconnecting the turns, whereby a firsthalf of the angular aperture of the annular strip whereon the secondaryextends is first traversed, for example in the trigonometric directionin the figure, then the return path is traversed in the clockwisedirection so as to approach the input end E1, then the other half of theangular aperture of the annular strip whereon the secondary extends istraversed, retaining the clockwise direction of rotation, and then thereturn path is traversed in the trigonometric direction so as toapproach the electrical terminal end E2 towards the electrical startingend E1, and thereby close the measurement circuit as for the secondaryin FIG. 20A.

FIGS. 20B and 20D are front views schematically representing an exampleof an embodiment of a transducer of an inductive linear displacementtransducer. The sensors in FIGS. 20B and 20D are sensors wherein atarget (not shown) comprising N conductive patterns is suitable formoving in translation along a rectilinear direction x with respect tothe transducer. The sensor in FIG. 20B is for example of the same typeas the sensor in FIG. 20A, adapted to a linear configuration, whichessentially consists of “unwinding” the circular annular strips of thesensor in FIG. 20A and replacing the conductive patterns and turns inthe shape of an annular strip sector, by conductive patterns and turnshaving a general rectangular or square shape. The sensor in FIG. 20D isfor example of the same type as the sensor in FIG. 20C, adapted to alinear configuration. In FIGS. 20B and 20D, only one secondary winding213 of each sensor has been shown, the embodiment of the target, theprimary winding, and, optionally, one or a plurality of additionalsecondary windings spatially offset with respect to the winding 213being within the grasp of those skilled in the art on the basis of theexplanations in the present description. By way of example and unlikethe primary winding of the angular sensors in FIGS. 20A and 20C, anexample of primary winding obtained when the set of two concentric turns101 a and 101 b for example described for the sensor in FIG. 1A is“unwound”, consists for example of a single turn for a linear sensor asdescribed in FIGS. 20B and 20D, optionally consisting of a plurality ofrevolutions. The turn of the primary winding has for example a generalrectangular shape, of dimension along y similar to the dimension along yof the conductive patterns of the target and/or of the turns of thesecondary as described above, and of dimension along x greater than thedimension along x of the conductive patterns of the target and/or of theturns of the secondary, so that the contribution to the overallelectromagnetic field distribution, created at the primary branchesoriented along y and which are situated at both ends along x of theprimary, are relatively attenuated in the vicinity of the secondarybranches oriented along y and which are situated at both ends along x ofthe secondary. In particular, for a transducer with a single secondarywinding, the range along x of the primary will be greater than the rangealong x of the secondary, and preferably but not exclusively, greater byat least one electrical half-period of the sensor, distributed equally(at one quarter of an electrical period) at each end of the sensor. As ageneral rule, a preferred example of embodiment of the primary windingof an inductive linear displacement sensor is a turn having arectangular general shape and a range greater than the overall range ofthe set of secondaries, for example but not exclusively, greater by atleast one electrical half-period of the sensor, distributed equally (atone quarter of an electrical period) at each end of the sensor.

In the examples in FIGS. 20B and 20D, the sensors comprise N=6 polepairs. However, the embodiments described are not restricted to thisparticular case.

In the example of the sensor in FIG. 20D, the secondary winding 213extends into a zone having a dimension D_(tot) parallel with the degreeof freedom of the sensor, i.e. parallel with the direction x ofdisplacement of the target with respect to the transducer. The winding213 comprises 2N loops or turns of alternating winding directionselectrically connected in series between the ends E1 and E2 thereof.More particularly, the winding 213 comprises N loops or turns 213 _(i+)having the same first winding direction, and N loops or turns 213 _(i−)having the same second winding direction opposite the first direction,each turn 213 _(i+) or 213 _(i−) having a dimension along the directionx approximately equal to an electrical half-period of the sensor (i.e.for example approximately equal to D_(tot)/2N), and the turns 213 _(i−)and 213 _(i+) being juxtaposed in pairs in alternation along the zone ofdimension D_(tot) of the secondary winding.

According to a second embodiment, the secondary winding consists of:

a first coiled conductive section 213A forming N half-turns ofalternating directions, extending between a first end E1 of the winding,situated approximately at the midpoint of the distance D_(tot) alongwhich the winding 213 extends parallel with the direction x, and a firstintermediate point A of the winding, situated at a first end of thedistance D_(tot);

a second coiled conductive section 213B forming N half-turns ofalternating directions, complementary to the N half-turns of the section213A, extending between the point A and a second intermediate point M ofthe winding, approximately at the midpoint of the distance D_(tot);

a third coiled conductive section 213C forming N half-turns ofalternating directions, extending between the point M and a thirdintermediate point B of the winding, situated at the second end of thedistance D_(tot); and

a fourth coiled conductive section 213D forming N half-turns ofalternating directions, complementary to the N half-turns of the section213C, extending between the point B and a second end E2 of the winding,situated approximately at the midpoint of the distance D_(tot), in thevicinity of the first end E1 of the winding.

More particularly, in the example shown, in the left part of the winding(in the orientation of the figure), the section 213A comprises NU-shaped half-turns wherein the vertical branches are oriented inopposite directions along a direction y approximately normal to thedirection x, and the section 213B comprises N U-shaped half-turnswherein the vertical branches are oriented alternately in oppositedirections along the direction y. Each U-shaped half-turn of the section213A has the vertical branches thereof approximately aligned with thevertical branches of a U-shaped half-turn of opposite orientation of thesection 213B. The sections 213C and 213D are arranged according to asimilar arrangement in the right part of the winding. As such, in thisexample, the portions of the winding 213 orthogonal to the direction ofdisplacement x are traversed twice and twice only by the wire or trackof the winding (except for the two orthogonal end portions of thewinding situated at both ends of the distance D_(tot), which, in thisexample, are traversed a single time—this exception does not arisehowever in the case of an angular sensor of angular aperture of 360°,wherein all the radial portions of the primary winding can be traversedtwice and twice only by the wire or track of the winding), and theportions of the winding 213 parallel with the direction of displacementx are traversed once and once only by the wire or track of the winding.

In terms of path travelled by the constituent electrical circuit of thepatterns of the secondary winding, the embodiment of the solution inFIG. 20D corresponds to the embodiment of a solution of the typedescribed with reference to FIG. 20B, and by linear-angulartransposition also corresponds to the embodiment of the solutions inFIGS. 20A and 20C. On the other hand, the sequence whereby this path istravelled differs between the transducer in FIG. 20D (and bytransposition the transducer in FIG. 20C), and the transducer in FIG.20B (and by transposition the transducer in FIG. 20A). In particular,the arrangement described with reference to FIGS. 20D and 20A isdesigned so as to show an intermediate connection point M between theends E1 and E2.

The winding 213 can be provided, in addition to the connection terminalsPE1 and PE2 at the ends E1 and E2 thereof, with a third access terminalPM connected to the midpoint M of the winding.

In the case of multi-pole sensors comprising an even number N of polepairs, and as represented in FIG. 20D, the secondary winding has as manyturns 213 _(i+) (referred to as positive) on the right as turns 213_(i+) on the left (N/2 on each side), and consequently the secondarywinding has as many turns 213 _(i−) (referred to as negative) on theright as turns 213 _(i−) on the left (N/2 on each side).

One advantage of the secondary winding arrangement in FIG. 20D when thenumber of pole pairs adopts an even value, lies in that the induction issubstantially identical, to the nearest sign, regardless of the positionof the target with respect to the transducer, on the two portions E1-Mand E2-M on either side of the midpoint, while enabling the threeconnections E1, E2 and M to be situated adjacent to one another.

This preferred embodiment wherein the number of pole pairs adopts evenvalues is in no way exclusive of other embodiments. Alternatively, ifthe number N of pole pairs is high, the choice of an odd number N isperfectly acceptable insofar as the error of signal symmetry between theportion E1-M and the portion E2-M varies as an inverse function of N.

The inventors observed that when the sensor is embodied according to thesecond embodiment, if the midpoint M of the winding is referenced at agiven electric potential of the differential measurement means, forexample at a constant potential centered on the voltage measurementrange of the measurement means, the common mode component contained inthe electrical signal present at the terminals of the dipole E1-E2,which does not carry useful information on the position and thedisplacement of the target with respect to the transducer, is low withrespect to the differential mode component contained in the sameelectrical signal present at the terminals of the dipole E1-E2, thedifferential mode component carrying however, the useful information onthe displacement of the target with respect to the transducer. Thearrangement of the sensor in FIGS. 20C and 20D suitable for positioningthe midpoint M in the immediate vicinity of the ends E1 and E2 thereforehas a definite advantage, for example with respect to the arrangement ofthe sensor in FIG. 20B wherein the midpoint M is removed from the endsE1 and E2, and more generally with respect to the arrangement of thesensors in FIGS. 20A and 20B wherein the values E1-M and E2-M aredependent on the position of the target with respect to the transducer,or, in other words, with respect to the sensor arrangements wherein theratio of the common mode component over the differential mode componentat the terminals of a secondary winding is not low and variessignificantly with the position of the target with respect to thetransducer.

In particular, one advantage of the sensors described in FIGS. 20C and20D when the midpoint M is suitably connected to the measurement means,lies in high immunity of the two electric potentials at the ends E1 andE2, to the component of the electromagnetic excitation field (primary)which does not vary with the position, whereas the spatiallydifferential nature of the measurement of the sensor in FIG. 7 onlyguarantees immunity on the difference in potential at the ends E1 andE2.

In addition to the immunity to the “direct” field emitted by the primary(internal source of the system), the sensors in FIGS. 20C and 20D alsooffer increased immunity to electromagnetic and/or electrostaticdisturbances emitted by an external source at the transduction zone andwherein the spatial distribution is relatively homogeneous, or moregenerally increased immunity to any form of electromagnetic and/orelectrostatic disturbance with respect to sensors as described in FIGS.20A and 20B.

Examples of practical examples of increased immunity to externaldisturbances in the transduction zone are for example the reduction ofconstraints on electronic measurement means protections, such as voltagesurge protections, and/or the relaxation of design constraints onelectrical signal conditioning systems, such as the common moderejection rate of differential amplifiers.

It should be noted that adapting an inductive sensor to apply a midpointaccording to the second embodiment can give rise to an increase in thenumber of interfaces of the conditioning circuit (for example the numberof tabs of an integrated circuit). It should particularly be noted thataccording to the prior art of inductive measurement, it tends to beconventional to minimize the number of physical interfaces bysubstituting same with electronic or digital processing. However, thissecond embodiment makes it possible to achieve a relatively simpleelectronic solution, of high immunity and measurement robustness levelsthan with known solutions.

FIG. 20E is a “small signal” electrical representation of the effectiveinduction phenomena V_(M1) and V_(M2), i.e. of the signals carrying theinformation or a portion of the information on the position and/ordisplacement of the target with respect to the transducer, and parasiticinduction phenomena V_(P), V_(P)′, et V_(P)″ at the connection wiresbetween the terminals E1, E2 and M of the transducer, and the terminalsPE1, PE2 and PM for example connected at the external electrical means.In this figure, and inasmuch as the wires connected from E1, E2 and Mfollow each other in close succession, the common mode disturbancesV_(P), V_(P)′, and V_(P)″ are substantially equal and are substantiallyoffset in the measurements V_(PE1) (made at the terminals of the dipolePM-PE1) and V_(PE2) (made at the terminals of the dipole PM-PE2) on onehand, and in the measurement V_(PE1PE2) made at the terminals of thedipole PE1-PE2 on the other. Once the potential of the terminal PM setto a known value V_(REF), the signals measured at the terminals of thetripole (PE1, PE2, PM) become extremely immunized to externalelectromagnetic interference in the connection zone between theterminals of the transducer (E1, E2, M) and the connection terminals forthe external electrical means (PE1, PE2, PM), firstly by limiting therisks of overvoltage on the inputs of the electrical means (the signallevels remain within the range of the conditioning means, and themeasurement is unconditionally valid), and secondly by relaxingrequirements on the common mode rejection rate of the differentialmeasurement V_(PE1PE2) (the measurement error introduced by thedisturbances is low). For example, it is possible to apply to theterminal PM a reference voltage of the conditioning block, or half thepower supply range of the conditioning block, or the electronic ground,without these embodiments being exclusive of other embodiments such asfor example the connection of the terminal PM or M directly to apotential of the transducer such as the ground.

A representative signal of the position of the target with respect tothe transducer is thereby obtained, particularly robust to disturbancesand/or to parasitic coupling effects, whether they occur at thetransduction zone or the connection zone between the transducer andexternal electrical means, and whether they are inductive in nature asshown in the electrical diagram in FIG. 20E, or capacitive in naturewith the electrical environment of the transducer and/or the primarywinding or in particular the portions close to the hot spot of theprimary (high voltage).

Moreover, in the case where the transducer comprises a plurality ofspatially offset secondary windings (for example as described withreference to FIG. 5), the various windings can be arranged in and/or onvarious overlaid support layers each comprising one a plurality ofmetallization levels. This configuration, though satisfactory for manyapplications, can however pose problems in respect of robustness andprecision. Indeed, as a result, the median planes of the varioussecondary windings are situated at slightly different distances from theprimary winding and the target. This results in particular, firstly, ina difference in transduction gain, and therefore a difference in outputsignal level of the various secondary windings, and secondly indifferent linearity characteristics between a plurality of secondarywindings of the same transducer.

To solve this problem, it is preferably envisaged, as illustrated byFIGS. 21A, 21B, 22A and 22B by way of non-restrictive example, todistribute the various secondary windings of the transducer into twometallization levels, for example in the same support layer with twometallization levels, such that, for each winding, the length of trackor wire of the winding arranged in the first metallization level isapproximately equal to the length of track or wire of the windingarranged in the second metallization level. Preferably, a sustainedalternation of the changes of metallization plane is envisaged, suchthat a secondary track cannot travel, on the same plane, a distance (forexample an angular aperture in the case of an angular sensor) greaterthan an electrical half-period. In a preferred embodiment, themetallization plane transition zones are located such that there is asymmetric and/or anti-symmetric relationship between most of the trackportions arranged on the first metallization level, and most of thetrack portions arranged on the second metallization level, asillustrated in FIGS. 21A, 21B, 22A and 22B.

As such, the median planes of the various secondary windings are mergedand correspond to a virtual intermediate plane situated between thefirst and second metallization levels. This gives each electromotiveforce induced at the terminals of each secondary, a response accordingto the position of the target substantially identical in terms ofamplitude and linearity, to that of the electromotive forces induced atthe terminals of the other secondaries.

It should be noted that the examples of embodiments shown in FIGS. 21A,21B, 22A and 22B correspond to sensors of angular range D_(tot)=360°,i.e. wherein the angular range occupied by each secondary has an angularaperture substantially equal to a complete revolution. These examplesare exclusive of alternative embodiments involving sensors of angularaperture strictly less than 360°, for example less than 180° in order toenable assembly “from the side” of the transducer about a rotary shaft,rather than a “through” assembly of the sensor about said shaft in thecase of a sensor of angular aperture 360° as described in FIGS. 21A,21B, 22A and 22B for example. Under these conditions, it is reiteratedmoreover that the angular aperture of the target can alternativelyretain a value of 360° independently of the angular aperture adopted bythe secondary/secondaries of the transducer, or adopt a value less than360° and for example adapted to the angular displacement range of theapplication.

FIGS. 21A and 21B are front views schematically representing an exampleof an embodiment of a transducer with two secondary windings 223 (hollowline) and 223′ (solid line) spatially offset by a quarter of anelectrical period, for an inductive angular displacement sensor. In theexample shown, the number N of pole pairs of the sensor is equal to 6,and each secondary winding 223, 223′ comprises 2N=12 loops or turns. Theembodiments described are not however restricted to this specific case.In this example, the two secondary windings 223 and 223′ are formed inand on the same substrate with two metallization levels M1 and M2connected by conductive vias (schematically represented by circles). Foreach winding, the length of track formed in the level M1 isapproximately equal to the length of track formed in level M2. FIG. 21Ais a front view of the metallization level M1, and FIG. 21B is a frontview of the metallization level M2. The patterns of the level M1 aresubstantially found on the basis of the patterns of the level M2 byantisymmetry with respect to an intermediate plane between the medianplanes of the levels M1 and M2.

The windings 223 and 223′ each have, viewed from above, an arrangementof the type described with reference to FIG. 20C (i.e. an arrangement ofthe type described with reference to FIG. 20D adapted to an angularconfiguration, the coiling principle described with reference to FIG.20D applying in a similar manner, the distance D_(tot) no longer being alinear distance but now being an angular distance, equal to 360°).

As such, the winding 223 comprises:

a first curved coiled conductive section 223A forming N half-turns ofalternating directions, extending along a first circular annularhalf-strip in the example shown between a first end E1 of the winding223, situated approximately at the midpoint of the distance D_(tot) (forexample in the vicinity—i.e. within 5° and preferably with 2°—of anangular position to which the value 0° is arbitrarily assigned), and anintermediate point A of the winding, situated at a first end of thedistance D_(tot) (for example in the vicinity of the angle 180°);

a second curved coiled conductive section 223B forming N half-turns ofalternating directions, complementary to the N half-turns of the section223A, extending along the first annular half-strip between the point Aand a second intermediate point M of the winding, situated approximatelyat the midpoint of the distance D_(tot) (for example in the vicinity ofthe angle 0°);

a third curved coiled conductive section 223C forming N half-turns ofalternating directions, extending along a second annular half-stripcomplementary with the first half-strip between the point M and a thirdintermediate point B of the winding, situated at an opposite end of thedistance D_(tot) (for example in the vicinity of the angle−180°); and

a fourth curved coiled conductive section 223D forming N half-turns ofalternating directions, complementary to the N half-turns of the section223C, extending along the second annular half-strip between the point Band a second end E2 of the winding, situated approximately at themidpoint of the distance D_(tot) (in this example in the vicinity of theangle 0°).

As seen in FIGS. 21A and 21B, in this (non-restrictive) example, theportions of the winding 223 orthogonal to the direction of displacementof the target with respect to the sensor, i.e. the radial branches ofthe winding, are traversed twice and twice only by the wire or track ofthe winding, and the portions of the winding 223 parallel with thedirection of displacement of the target with respect to the sensor, i.e.the ortho-radial branches of the winding, are traversed once and onceonly by the wire or track of the winding.

More particularly, in this example: the radial portions positioned atangles offset by 0° modulo an electrical half-period, with respect tothe angle characterizing the end E1, are traversed twice and twice onlyby the wire or track of the winding 223; the radial portions positionedat angles offset by a quarter of an electrical period modulo anelectrical half-period, with respect to the angle characterizing the endE1, are traversed twice and twice only by the wire or track of thewinding 223′; and the ortho-radial portions are traversed once and onceonly by the wire or track of the winding 223, and once and once only bythe wire or track of the winding 223′.

This embodiment makes it possible to contain over two planes and onlytwo metallization planes, two secondaries as described in the precedingsolutions, i.e. without making any concession on the overall shape ofthe patterns of each secondary. It should be noted that the embodimentsshown in FIGS. 21A, 21B, 22A and 22B implement two secondaries arrangedover two metallization planes, but are in no way exclusive of furtherembodiments such as an embodiment implementing for example threesecondaries arranged over three metallization planes.

In this example, each of the U-shaped half-turns of each of the sections223A, 223B, 223C and 223D of the winding 223 (hollowed line) hasapproximately half of the length thereof in the metallization level M1and the other half of the length thereof in the metallization level M2.A change of level occurs approximately every L/2 meters of conductivetrack, where L denotes the length of a turn of the winding, consistingof the connection in series of two complementary U-shaped half-turns. Inthe example shown, the level change points of the winding are situatedat the midpoints of the ortho-radial branches (or horizontal branches)of the U shapes forming the half-turns. However, the embodimentsdescribed are not restricted to this specific case. In FIGS. 21A and21B, the numbers ranging from c1 to c28 denote, in the order of travelbetween the terminals E1 and E2, different portions of the winding 223.

The secondary winding 223′ (solid line) is arranged in the levels M1 andM2 according to an arrangement substantially identical to that of thewinding 223, but with an angular offset of approximately a quarter of anelectrical period (i.e. 15° in this example) with respect to the winding223.

It should be noted that in the structure in FIGS. 21A and 21B, theconnection tracks to the ends E1 and E2 of the winding 223 can forexample be situated respectively in the metallization levels M1 and M2,and be overlaid on one another. This makes it possible to minimize theparasitic coupling difference on each of these branches with any sourceof external induction (connection track to the primary, externalelectromagnetic disturbance, etc.). An access track to the midpoint M ofthe winding can be situated in a third metallization level (not shown),overlaid on the access tracks to the terminals E1 and E2 which aresituated in the metallization levels M1 and/or M2, to be situated in oneof the metallization levels M1 and M2, slightly offset with respect tothe access tracks to the terminals E1 and E2. A similar arrangement ofthe access tracks to the corresponding terminals E1′, E2′ and M′ of thewinding can be envisaged for the winding 223′. More generally,regardless of the arrangement of the access tracks, so as to increasethe immunity to electromagnetic disturbances between the transductionzone (secondary) and the access and/or connection terminals to thesignal conditioning means, it is preferably sought to keep the pathsfrom the ends E1 and E2 as close as possible (for example overlaid inPCB technology), and to a lesser degree position the path from theintermediate point M relatively close to the paths from the ends E1 andE2.

It should be noted further that, in the example in FIGS. 21A and 21B,besides the vias making changes in metallization levels of the windings223 and 223′, and the conductive tracks travelling in each metallizationlevel for field pickup purposes, vias or conductive filling chips, withno electrical connection function between field pickup tracks, have beenregularly distributed along the windings 223 and 223′. These conductivefilling patterns have the role of symmetrizing the conductive structureof the transducer, so as to periodize the influence thereof on thespatial distribution of the field, and more particularly of minimizingthe field distribution singularities which would be conveyed by avariation of the secondary output signal according to the position. Theaddition of these conductive filling patterns is however optional. Inparticular, if the vias making the changes of metallization level havesmall dimensions with respect to the skin thickness, the operatingfrequency, the constituent material thereof, it is possible to envisagenot adding the conductive chips and in particular not performing thedrilling thereof, which can reduce the cost of the device.

FIGS. 22A and 22B are front views schematically representing analternative embodiment of a transducer of the type described withreference to FIGS. 21A and 21B. This alternative embodiment differs fromthe example in FIGS. 21A and 21B in that, in the example in FIGS. 22Aand 22B, the changes of metallization level are more numerous than inthe example in FIGS. 21A and 21B. As such, in the example in FIGS. 22Aand 22B, instead of a change of metallization level every L/2 meters ofconductive track of the secondary winding, where L is the length of aturn of the winding, it is envisaged to make k changes of metallizationlevel every L/2 meters of track, where k is an integer greater than orequal to 2. The number k can be chosen accounting for the internal andexternal radii of the transducer. By way of non-restrictive example, forgiven sensor sizes and when the changes of level are made only in theortho-radial portions of the turns, k can be chosen as great as itpossible to place adjacent (for example equi-distributed) vias overother-radial portions without these vias short-circuiting. For thepurposes of simplification, FIGS. 22A and 22B show an example of anembodiment for a sensor with N=2 pole pairs, wherein the transducercomprises 2 secondary windings 233 (dashed line) and 233′ (solid line)angularly offset by a quarter of the electrical period of the sensor(i.e. 360°/4N=45° in this example). The alternative embodiment in FIGS.22A and 22B is however compatible with sensors comprising a greaternumber of pole pairs. As in the example in FIGS. 21A and 21B, conductivefilling patterns with no electrical connection function can be envisagedto symmetries the structure further.

Third Aspect

In the examples of embodiments of multi-pole sensors hitherto described,for a given dimension D_(tot) of a secondary winding of the transducerparallel with the degree of freedom of the target with respect to thesensor, and for a given number N of pole pairs, the maximum extent ofthe range of positions suitable for being detected by the sensor isapproximately one electrical half-period (for example D_(tot)/2N i.e.360°/2N in the case of an angular sensor) if the sensor comprises asingle secondary winding, and can increase to approximately oneelectrical period (for example D_(tot)/N i.e. 360°/N in the case of anangular sensor) if the sensor comprises more than one secondary winding,for example if it comprises two identical secondary windings spatiallyoffset by a quarter of an electrical period (for example D_(tot)/4N,i.e. 360°/4N in the case of an angular sensor), or if it comprises threeidentical secondary windings spatially offset by a sixth of anelectrical period (for example D_(tot)/6N, i.e. 360°/6N in the case ofan angular sensor). In any case, the multi-pole angular displacementsensors of the type described above do not make it possible to makedisplacement measurements over a complete revolution (360°) absolutely,i.e. without using displacement log memorization methods, and/or methodsfor referencing the position at start-up and/or during the operation ofthe sensor. This remark is valid regardless of the number N of polepairs greater than or equal to 2, and can be more problematic when thenumber N is high, for example N≥4 and preferably N≥6. The inductivelinear displacement sensors described above have the same limitationsand do not make it possible to make a measurement over the completerange of D_(tot) absolutely.

According to a third aspect, it is sought to embody an inductivedisplacement sensor such that, for a given number N of pole pairs, for agiven dimension D_(tot) of the secondary winding(s) of the transducerparallel with the degree of freedom of the sensor, the sensor issuitable for detecting the position of the target with respect to thetransducer substantially over the entire range D_(tot) of thetransducer. In particular, in the case of an angular position sensor, itis sought to embody a sensor suitable for detecting the position of thetarget with respect to the transducer over a complete revolution, i.e.over an angular range of approximately 360°, even when the number N ofthe pole pairs of the sensor is high, for example N≥4 and preferablyN≥6.

FIG. 23 is a front view schematically representing an example of amulti-pole inductive angular displacement sensor. In FIG. 23, only thetarget of the sensor has been shown.

The target of the sensor in FIG. 23 comprises, as in the example in FIG.3B, N conductive patterns 117 _(i) (N=6 in the example shown) regularlydistributed along the 360° of a first circular annular strip 118 of thetarget. Each conductive pattern 117 _(i) has the shape of a portion orof a sector of the first annular strip 118, of angular aperture α_(N)approximately equal to D_(tot)/2N=360°/2N, two consecutive patterns 117_(i) being separated by a sector of the first annular strip 118,substantially of the same angular aperture α_(N). The target of thesensor in FIG. 23 further comprises N+1 conductive patterns 119 j, wherej is an integer ranging from 1 to N+1, regularly distributed along the360° of a second circular annular strip 120 of the target, concentricwith the first strip 118 and not overlaid with the first strip 118. Inthe example shown, the second annular strip has an internal radiusgreater than the external radius of the first annular strip. Eachconductive pattern 119 _(j) has the shape of a sector of the secondannular strip 120, of angular aperture α_(N+1) approximately equalD_(tot)/2(N+1)=360°/2(N+1), two consecutive conductive patterns 119 _(j)being separated by a sector of the second annular strip 120,substantially having the same angle α_(N+1).

The transducer (not shown for simplification purposes) of the sensor inFIG. 23 corresponds with the target shown, i.e. it comprises:

one or a plurality of primary windings suitable for producing a magneticexcitation in first and second circular annular strips of the transducersubstantially identical to the first and second annular strips 118 and120 of the target, intended to be positioned respectively facing thefirst and second annular strips 118 and 120 of the target;

at least first and second secondary windings of electrical periodD_(tot)/N (for example 360°/N in the example of an angular sensor), eachcomprising N turns of the same winding direction, in the shape ofsectors of angular aperture α_(N) of the first annular strip of thetransducer, regularly distributed along the first annular strip of thetransducer, or, alternatively, comprising 2N turns of alternatingwinding directions in the shape of sectors of angular aperture α_(N) ofthe first annular strip of the transducer, regularly distributed alongthe first annular strip of the transducer; and

at least third and fourth secondary windings of electrical periodD_(tot)/(N+1) (for example 360°/(N+1)), each comprising N+1 turns of thesame winding direction in the shape of sectors of angular apertureα_(N+1) of the second annular strip of the transducer, regularlydistributed along the second annular strip of the transducer, or,alternatively, comprising 2(N+1) turns of alternating winding directionsin the shape of the sectors of angular aperture α_(N+1) of the secondannular strip of the transducer, regularly distributed along the secondannular strip of the transducer.

Preferably, in the first annular strip, the second secondary winding ofelectrical period D_(tot)/N is substantially identical to the firstwinding and spatially offset by a quarter of an electrical period(D_(tot)/4N) with respect to the first winding, and, in the secondannular strip, the fourth secondary winding of electrical periodD_(tot)/(N+1) is substantially identical to the third winding andspatially offset by a quarter of an electrical period (D_(tot)/4(N+1))with respect to the second winding. More generally, the transducer cancomprise, in the first annular strip, a plurality of secondary windingsof electrical period D_(tot)/N, substantially identical to the firstwinding and spatially offset with respect to one another by a certainelectrical period percentage, and, in the second annular strip, aplurality of secondary windings of electrical period D_(tot)/(N+1),substantially identical to the third winding and spatially offset withrespect to one another by a certain electrical period percentage.

The operation of the sensor in FIG. 23 will now be described withreference to FIG. 24. The (non-restrictive) case is taken intoconsideration where the transducer of the sensor comprises, in the firstannular strip of the transducer, a first pair of identical secondarywindings of electrical period 360°/2N, spatially offset by a quarter ofan electrical period, and, in the second pair of identical secondarywindings of electrical period 360°/2(N+1), spatially offset by a quarterof an electrical period. As described above, this sensor is suitable forsupplying two sets of two separate electromotive forces, from which itis possible to construct an estimation of position respectively over aposition range equal to 360°/2N and over a position range equal to360°/2(N+1).

FIG. 24 is a diagram representing the progression, according to theposition of the target with respect to the transducer, of the estimationθ_(N) (solid line) of the position obtained using the electromotiveforces measured at the terminals of the first pair of secondarywindings, and of the estimation θ_(N+1) (dashed lines) of the positionobtained using the electromotive forces measured at the terminals of thesecond pair of secondary windings of the transducer.

As seen in FIG. 24, when the angular position θ of the target withrespect to the transducer varies from 0° to 360°, the positionestimation signal θ_(N) varies periodically between a low valuesubstantially equal to 0 and a high value substantially equal to 1 (theposition estimations are standardized herein for the purpose ofsimplification, the embodiments described not being restricted to thisparticular case), with a variation period equal to the electrical periodof the first pair of secondary windings, i.e. equal to 360°/N=60° forN=6. Furthermore, the position estimation signal θ_(N+1) variesperiodically between the low 0 and high values 1, with a variationperiod equal to the electrical period of the second pair of secondarywindings, i.e. equal to 360°/N+1≈51.4° for N=6.

By combining the levels of the position estimation signals θ_(N) andθ_(N+1), two separate measurement scales are obtained over a completesensor revolution, i.e. two different splits of the same range of 360°.The principle of a vernier applied to these two angular measurementscale, i.e. the construction of the difference θ_(N+1)−θ_(N) between thetwo standardized position estimations θ_(N+1) and θ_(N), is suitable forestimating the position and/or the displacement of the target relativeto the transducer over the entire distance D_(tot)=360° (i.e. over acomplete revolution).

More particularly, one of the position estimation signals, for examplethe signal θ_(N), can be used to provide “refined” target displacementinformation in N angular ranges restricted to the electrical period360°/N, and the difference θ_(N+1)−θ_(N) between the other positionestimation signal (the signal θ_(N+1) in this example) and this signalcan be used to provide rough absolute information of the position of thetarget over a complete revolution. Under these conditions, the roughabsolute information makes it possible to adapt the refined butangularly restricted information, so as to carry out an absolute andrefined displacement estimation over 360°.

One advantage of the sensor in FIG. 23 is that it makes it possible tobenefit to a certain degree of the advantages of multi-pole sensors,particularly in terms of robustness to positioning errors, while beingsuitable for providing measurements over an extended position range withrespect to the multi-pole sensors of the type described above.

As a general rule, it should be noted that the embodiment describedabove can be adapted to two signals θ_(N1) and θ_(N2), N1 and N2 beingdifferent integers not necessarily exhibiting a unitary difference.Under these conditions, a sensor characterized by N1 and N2=N1+2,exhibiting a similar arrangement to the arrangement of the sensor inFIG. 23, is suitable for extending the absolute measurement over a rangeD_(tot)/N=180°. As a general rule, a sensor characterized by N1 andN2=N1+r, where r is a positive integer strictly less than N1, makes itpossible under certain conditions to extend the absolute measurementover a range D_(tot)/k=360°/r.

In this general case, r is obviously a strictly positive integer, i.e.different to zero (or greater than or equal to 1), such that N2 isgreater than or equal to N1+1. If r was not strictly positive, N2 couldbe equal to N1 if r=0, and the two signals θ_(N1) and θ_(N2) would beidentical (not distinct) and would not be suitable for estimating theabsolute position by the difference between the two standardizedposition estimations, as explained above.

Furthermore, r is an integer less than or equal to N1−1, such that N2 isless than or equal to 2N1−1. If N2 could be equal to 2N1, the differencebetween the two standardized position estimations, as described above,would furnish information similar to that furnished solely by the firstset of patterns (corresponding to N1), and would not be suitable forbetter estimating the absolute difference by the two standardizedposition estimations. As such, once r is less than or equal to N1−1, theembodiments and advantages of the invention are applicable.

In practice, r has a preferably low value, for example r is equal to 1as described above and illustrated in FIG. 23. This makes it possible tomake an absolute measurement over the greatest range, 360°. In someapplications, it can be preferable to choose a value of r equal to 2(absolute measurement over 180° when D_(tot)=360°), or choose a value ofr equal to 3 (absolute measurement over 120° when D_(tot)=360°), orchoose a value of r equal to 4 (absolute measurement over 90° whenD_(tot)=360°), or choose a value of r equal to 5 (absolute measurementover 72° when D_(tot)=360°), etc.

The sensor in FIG. 23 poses a number of problems, however. Inparticular, the size of the sensor is increased with respect to a sensorof the type described above. Indeed, in the example in FIG. 23, the“effective” transducer surface area for making a measurement is that ofa circular annular strip approximately two times greater in width thanthat of the “effective” annular strip of a transducer of the typedescribed with reference to FIG. 3A. Similarly, the “effective” targetsurface area for making a measurement is that of an annular stripapproximately two times greater in width than that of the “effective”annular strip of the type described with reference to FIG. 3B.Furthermore, the embodiment of the primary is more complex than in thepreceding embodiments if it is sought to excite in a relatively uniformmanner each of the annular strips of scale N and N+1 of the sensor. Inpractice, it can be necessary to use three sets of separate turns toembody the primary excitation winding.

FIG. 25 is a front view schematically representing an example of anembodiment of an inductive displacement sensor. The sensor in FIG. 25 isa multi-pole sensor with two measurement scales N and N+1, operatingaccording to the principle of a vernier as described with reference toFIGS. 23 and 24. In FIG. 25, only the target of the sensor has beenshown.

The target of the sensor in FIG. 25 comprises a plurality of separatedconductive patterns 127 _(i), distributed along the 360° of a circularannular strip 130 of the target. As seen in FIG. 25, the set of patternsformed by the conductive patterns 127 _(i) is not periodic. The variousconductive patterns 127 _(i) have the shape of angular sectors, ofdifferent angular apertures, of the annular strip 130 of the target, andare in principle irregularly distributed along the annular strip 130.

The set of patterns formed by the conductive patterns 127 _(i) over theannular strip 130 of the target corresponds to the (virtual) overlay ofthe first and second sets of periodic conductive patterns of respectiveperiodicities 360°/N and 360°/(N+1). The first set of patterns comprisesN elementary patterns 129 _(j) (solid lines) regularly distributed alongthe annular strip 130 of the target, each elementary pattern 129 _(j)having the shape of a sector of the annular strip 130, of angularaperture approximately equal to 360°/2N. The second set of patternscomprises N+1 elementary patterns 131 _(k) (dashed lines), regularlydistributed along the annular strip 130, each elementary pattern 131 khaving the shape of a sector of the annular strip 130, of angularaperture approximately equal to 360°/2(N+1). In other words, the surfaceareas of conductive patterns of the target in FIG. 25 correspond to thetotal or the combination of the surface areas of the conductive patternsof a first target of the type described with reference to FIG. 3B, ofelectrical period 360/N, and of a second similar target, having the sameinternal and external radii as the first target, but having anelectrical period 360°/(N+1).

The transducer (not shown for the purpose of simplification) of thesensor in FIG. 25 is for example suitable for the conductive patterns ofthe target in a similar manner to that described with reference to theexample in FIG. 23. In particular, it comprises for example:

at least one primary winding suitable for producing an approximatelyuniform magnetic excitation in a circular annular strip of thetransducer substantially identical to the circular annular strip 130 ofthe target, intended to be positioned facing the annular strip 130 ofthe target;

at least first and second secondary windings of periodicity 360°/N,spatially offset by a fraction of an electrical period, extending alongthe circular annular strip of the transducer; and

at least third and fourth secondary windings of periodicity 360°/(N+1),spatially offset by a fraction of an electrical period, extending alongthe same annular strip of the transducer.

The inventors observed that, although the conductive patterns ofelectrical period 360°/N and 360°/(N+1) of the target overlap andshort-circuit one another, and consequently the target comprisesconductive patterns 127 _(i) irregularly distributed over a completerevolution of 360°, these patterns having residual angular apertureswhich may be different to the periodic angular apertures of the patternsof the sets of secondary windings of the transducer, the sensor in FIG.25 is suitable for making, with very good performances, displacementmeasurements over the entire distance D_(tot) (i.e. over a completerevolution) using a vernier type reading method similar or identical tothe method described with reference to FIGS. 23 and 24.

One advantage of the sensor in FIG. 25 is that, due to the overlay ofthe patterns of respective electrical periods 360°/N and 360°/(N+1), thesize of the sensor can be reduced with respect to a configuration of thetype described with reference to FIG. 23. Furthermore, a single primarywinding, for example of the type described with reference to FIG. 3A,suffices to generate a sufficiently uniform magnetic excitation forproper operation of the sensor.

FIG. 26 is a front view schematically representing an alternativeembodiment of the sensor in FIG. 25. In FIG. 26, only the target of thesensor has been shown.

The target of the sensor in FIG. 26 comprises a plurality of separatedconductive patterns 137 _(i), distributed along the 360° of a firstcircular annular strip 138 or wide strip of the target.

The set of patterns formed by the patterns 137 _(i) on the annular strip138 of the target corresponds to the overlay of the first and secondsets of periodic patterns of respective electrical periods 360°/N and360°/(N+1). The first set of patterns comprises N elementary conductivepatterns 139 _(j) (solid lines) regularly distributed along the firstannular strip 138 of the target, each elementary pattern 139 _(j) havingthe shape of a sector of the first annular strip 138 of the target, ofangular aperture approximately equal to one electrical half-period360°/2N. The second set of patterns comprises N+1 elementary patterns141 _(k) (dashed lines), regularly distributed along the second circularannular strip 142 or narrow strip of the target, concentric with theannular strip 138 and included in the annular strip 138, i.e. having aninternal radius greater than the internal radius of the first annularstrip, and/or an external radius less than the external radius of theannular strip 138. Each elementary pattern 141 _(k) has the shape of anannular sector of the annular strip 142 of the target, of angularaperture approximately equal to 360°/2(N+1). The width (radialdimension) of the second annular strip 142 of the target is preferablymarkedly less than the (radial) width of the first annular strip 138 ofthe target, for example two to twenty times less than the width of thefirst annular strip (the wide strip).

The transducer (not shown for the purpose of simplification) of thesensor in FIG. 26 is for example suitable for the conductive patterns ofthe target in a similar manner to that described with reference to theexamples in FIGS. 23 and 25. In particular, it comprises for example:

at least one primary winding suitable for producing an approximatelyuniform magnetic excitation in a first circular annular strip of thetransducer (wide strip) substantially identical to the first annularstrip 138 of the target, intended to be positioned facing the firstannular strip of the target;

at least first and second secondary windings of periodicity 360°/N,spatially offset by a fraction of an electrical period, extending alongthe first circular annular strip of the transducer (the wide strip); and

at least third and fourth secondary windings of periodicity 360°/(N+1),spatially offset by a fraction of an electrical period, arranged along asecond circular annular strip of the transducer (narrow strip),substantially identical to the second annular strip 142 of the targetand intended to be positioned facing the annular strip 142 of thetarget.

The operation of the sensor in FIG. 26 is similar to that of the sensorin FIG. 25. Preferably, in the sensor in FIG. 26, the secondarywinding(s) making the “refined” measurement as described above, arewindings wherein the turns have the shape of annular sectors of thewidest annular strip of the transducer (substantially identical to theannular strip 138 of the target). By the concept of refined measurement,it is understood that priority is given to design work to provide themeasurement made by the secondaries of the wide strip with performanceand robustness, optionally and to a certain degree, at the expense ofthe performance and robustness of the measurement made by thesecondaries of the narrow strip.

An additional advantage of the sensor in FIG. 26 with respect to thesensor in FIG. 25 is that it is more robust to positioning errorsbetween the target and the transducer than the sensor in FIG. 25. Inparticular, the measurement obtained at the terminals of the secondarywindings of the wide strip (preferably associated with the refinedmeasurement) is more robust to positioning errors between the target andthe transducer than the sensor in FIG. 25. Indeed, in the sensor in FIG.26, reducing the surface area of one of the measurement scales withrespect to the other makes it possible reduce to a certain degree, thecoupling created by the patterns of the narrow strip on the patterns ofthe wide strip at the target, particularly with respect to the target inFIG. 25 for which the mutual influence of one set of patterns on theother is substantially equivalent and very strong. It is therebypossible to increase the robustness of one of the sets of secondaries topositioning errors.

It should be noted that, in the example shown, the mean radius of thesecond circular annular strip of the sensor (the narrow strip) isapproximately equal to the mean radius of the first circular annularstrip of the target (the wide strip). This configuration is advantageousas it makes it possible to remove in a substantially equivalent mannerthe effects of the internal and external ortho-radial portions of theconductive patterns. The embodiments described are however notrestricted to this particular configuration.

FIGS. 27A to 27C are front views schematically representing a furtheralternative embodiment of the sensor in FIG. 25. More particularly, FIG.27A is a front view of the target, FIG. 27B is a front view of a portionof the transducer, and FIG. 27C is a front view of a further portion ofthe transducer. In practice, the two portions of the transducerrepresented separately in FIGS. 27B and 27C for illustration purposes,are rigidly connected and overlaid concentrically in a singletransducer, without the breakdown of the constituent elements of saidtransducer in these two figures foreseeing a particular distributionover a plurality of metallization levels.

The target of the sensor in FIGS. 27A to 27C comprises a plurality ofseparated conductive patterns 147 _(i), distributed along the 360° of afirst circular annular strip 148 or wide strip of the target.

The set of patterns formed by the conductive patterns 147 _(i) on thefirst annular strip 148 corresponds to the overlay of a first set ofperiodic patterns of electrical period 360°/N, and of second and thirdsets of periodic patterns of electrical periods 360°/(N+1). The firstset of patterns comprises N elementary conductive patterns 149 _(j)(solid lines) regularly distributed along the annular strip 148 of thetarget (wide strip), each elementary pattern 149 _(j) having the shapeof a sector of the strip 148, of angular aperture approximately equal to360°/2N. The second set of patterns comprises N+1 elementary conductivepatterns 151 _(k) (dashed lines), regularly distributed along a secondannular strip 152 of the target (narrow strip), concentric with thefirst annular strip 148 and included in the strip 148, i.e. having aninternal radius greater than the internal radius of the annular strip148, and an external radius less than the external radius of the annularstrip 148. In this example, the internal radius of the annular strip 152of the target is greater than the mean radius of the first annular strip148. This example of an embodiment is in no way restrictive, and inparticular the narrow strips 152 and 154 can be arranged differentiallyin the wide strip 148, without the mean radius of the wide strip 148representing an impassable limit for either of the narrow strips. Eachelementary pattern 151 _(k) has the shape of a second of the secondannular strip 152 of the target, of angular aperture approximately equalto 360°/2(N+1). The (radial) width of the annular strip 152 of thetarget is preferably low with respect to the width of the annular strip148 of the target, for example three to twenty times less than the widthof the first strip. The third set of patterns comprises N+1 elementaryconductive patterns 153 _(k) (dashed lines), regularly distributed alonga third annular strip 154 of the target (narrow strip), concentric withthe annular strip 148 and included in the annular strip 148. In thisexample, the external radius of the annular strip 154 of the target isless than the mean radius of the annular strip 148. The differencebetween the mean radius of the first annular strip 148 and the meanradius of the third annular strip 154 is for example approximately equalto the difference between the mean radius of the second annular strip152 and the mean radius of the first annular strip 148. Each elementarypattern 153 _(k) has the shape of a sector of the third annular strip154 of the target, of angular aperture approximately equal to360°/2(N+1). The width of the third annular strip is for exampleapproximately equal to the width of the second annular strip.Alternatively, the width of the third annular strip 154 is such that thesurface area of a pattern of the annular strip 154 is approximatelyequal to the surface area of a pattern of the annular strip 152. Thesetwo examples of embodiments are in no way restrictive.

As seen in FIG. 27A, the periodic patterns of periodicity 360°/(N+1) ofthe annular strip 154 of the target are spatially offset by 360°/2(N+1)with respect to the periodic patterns of periodicity 360°/(N+1) of theannular strip 152 of the target. As such, in the “empty” angular rangesof angular aperture 360°/(N+1) separating two adjacent elementaryconductive elements 151 _(k), extends approximately an elementarypattern 153 _(k), and, in the “empty” angular ranges of angular aperture360°/(N+1) separating two adjacent elementary conductive patterns 153_(k), extends approximately an elementary conductive pattern 151 _(k).In other words, substantially all the radial directions of the targetencounter an elementary conductive pattern 151 _(k) or an elementarypattern 153 _(k).

The transducer of the sensor in FIGS. 27A to 27C is for example suitablefor the conductive patterns of the target in a similar manner to thatdescribed with reference to the examples in FIGS. 23, 25 et 26. Itcomprises for example:

at least one primary winding 211 (FIG. 27B) suitable for producing anapproximately uniform magnetic excitation in a first circular annularstrip of the transducer substantially identical to the first annularstrip 148 of the target, intended to be positioned facing the annularstrip 148 of the target;

at least first and second secondary windings 243 (only one secondarywinding 243 has been shown in FIG. 27B) of electrical period 360°/N,each comprising N turns of the same winding direction or, alternatively,2N turns of alternating winding directions, each turn of the first andsecondary windings having the shape of a sector of angular aperture360°/2N of the first annular strip of the transducer, and the N or 2Nturns of each winding being regularly distributed along the 360° of thefirst annular strip of the transducer;

at least third and fourth secondary windings 253 (only one secondarywinding 253 has been shown in FIG. 27C) of periodicity 360/(N+1), eachcomprising N+1 turns of the same winding direction or, preferably,2(N+1) turns of alternating winding direction, each turn of the thirdand fourth secondary windings having the shape of a sector of angularaperture 360°/2(N+1) of a second annular strip of the transducer,substantially identical to the second annular strip 152 of the targetand intended to be positioned facing the strip 152 of the target, theN+1 or 2(N+1) turns of each winding being regularly distributed alongthe 360° of the second annular strip of the transducer; and

at least fifth and sixth secondary windings 255 (only one secondarywinding 255 has been shown in FIG. 27C) of periodicity 360°/(N+1), eachcomprising N+1 turns of the same winding direction or, preferably,2(N+1) turns of alternating winding directions, each turn of the fifthand sixth secondary windings having the shape of a sector of angularaperture 360°/2(N+1) of a third annular strip of the transducer,substantially identical to the third annular strip 154 of the target andintended to be positioned facing the annular strip 154 of the target,the N+1 or 2(N+1) turns of each winding being regularly distributedalong the 360° of the third annular strip of the transducer.

The third and fifth secondary windings are of opposite polarities, i.e.they are spatially offset by 360°/2(N+1) according to the polarityconvention (represented by a + or − sign) defined in FIG. 7 and adoptedhereinafter in the description. The fourth and sixth windings arearranged with respect to one another according to a substantiallyidentical arrangement to the arrangement between the third and fifthsecondary windings.

Preferably, in the first circular annular strip, the first and secondsecondary windings are spatially offset by 360°/2N with respect to oneanother, in the second circular annular strip, the third and fourthsecondary windings are spatially offset by 360°/2(N+1) with respect toone another, and, in the third circular annular strip, the fifth andsixth secondary windings are offset by 360°/2(N+1) with respect to oneanother.

More generally, the transducer can comprise, in the first annular strip,a plurality of secondary windings of electrical period D_(tot)/N,substantially identical to the first secondary winding and spatiallyoffset with respect to one another by a fraction of an electricalperiod; in the second annular strip, a plurality of secondary windingsof electrical period D_(tot)/(N+1), substantially identical to the thirdsecondary winding and spatially offset with respect to one another by afraction of an electrical period; and in the third annular strip, aplurality of secondary windings of electrical period D_(tot)/(N+1),substantially identical to the fifth secondary winding and spatiallyoffset with respect to one another by a fraction of an electricalperiod.

The operation of the sensor in FIGS. 27A to 27C is similar to that ofthe sensor in FIGS. 25 and 26.

Various reading configurations can be used in the example in FIGS. 27Ato 27C. The inventors particularly observed that:

reading of the set of patterns 147 _(i) by a secondary winding 243generates a wanted signal suitable for processing, of electrical period360°/2N;

reading of the set of patterns 147 _(i) by a secondary winding 253generates a wanted signal suitable for processing, of electrical period360°/2(N+1);

reading of the set of patterns 147 _(i) by a secondary winding 255generates a wanted signal suitable for processing, of electrical period360°/2(N+1);

a combination of the simultaneous readings of the set of patterns 147_(i) by a secondary winding 253 and by a secondary winding 255, forexample when both secondaries are of alternating polarities (asillustrated by FIG. 27C) and electrically connected in series, generatesa wanted signal suitable for processing, of electrical period360°/2(N+1) and of amplitude approximately equal to double the wantedsignal read by the secondary winding 253 or of the wanted signal read bythe secondary winding 255;

reading of the set of patterns 147 _(i) by a secondary winding 243generates a relatively weak parasitic signal (particularly ofperiodicities 360°/(N+1) and 360°) with respect to the wanted signaldetected by this secondary winding;

a combination of the simultaneous readings of the set of patterns 147_(i) by a secondary winding 253 and by a secondary winding 255, forexample when two secondaries are of alternating polarities (asillustrated by FIG. 27C) and electrically connected in series, generatesa relatively weak parasitic signal (particularly of periodicities 360°/Nand 360°) with respect to the wanted signal detected by this secondarywinding.

An additional advantage of the sensor in FIGS. 27A to 27C is that it iseven more robust to positioning errors between the target and thetransducer as the sensor in FIG. 26.

In particular, the measurement obtained at the terminals of thesecondary windings 243 of the wide strip (preferably associated with therefined measurement) is more robust to positioning errors between thetarget and the transducer than in the sensor in FIG. 26. Indeed, in thesensor in FIGS. 27A to 27C, substantially all the radial directions ofthe target encounter a single elementary conductive pattern of a narrowstrip, arranged on either of the two narrow strips of the target.Furthermore, the two narrow strips of the target are preferably arrangedat a sufficient distance from the two internal and external ortho-radialbranches of the secondaries 243 of the wide strip of the transducer.Under these conditions, the coupling of the conductive patterns of thetwo narrow strips of the target on the measurement at the terminals ofthe secondaries 243 of the wide strip results from the combination ofthe induction of the conductive patterns of a narrow strip of thetarget, these two contributions compensating each other substantiallyregardless of the position of the target with respect to the transducer.The parasitic coupling then adopts a relatively stable value when theposition of the target with respect to the transducer changes.Furthermore, the coupling adopts a substantially zero value when thesecondaries of the wide strip comprise 2N turns of alternating windingdirections, as described for the sensor in FIG. 3 for example, in orderto make a spatially differential measurement. A further formulationconsists of considering that the secondaries of the wide strip of thetransducer “see” roughly the two offset narrow strips as a single narrowmedian conductive strip and substantially solid or continuous overD_(tot) in electromagnetic terms (and not electrically), and that thisvirtual strip as such induces a substantially position-independentsignal at the terminals of said secondaries.

Moreover, the inventors observed that the measurement obtained at theterminals of the secondary winding 253 (of a narrow strip) exhibit abehavior according to the position of the target with respect to thetransducer which is similar to the behavior according to the position ofthe measurement obtained at the terminals of the secondary winding 255(of the other narrow strip). The inventors also observed that, in theevent of positioning defects of the target with respect to thetransducer, the behavior according to the position of the measurement atthe terminals of one of the two windings 253 or 255 of one of the twonarrow strips, exhibits deformations relatively complementary with thedeformations obtained on the measurement at the terminals of the otherwinding. As such, by combining the measurements of the two secondariesof the two narrow strips, and preferentially connecting the two windingsin series if they are designed so as to exhibit a relatively similarbehavior in respect of position in terms of amplitude and linearity inparticular, it is possible to obtain a measurement at the terminals ofthe new composite winding which is relatively robust to positioningdefects. Indeed, in the sensor in FIGS. 27A to 27C, substantially allthe radial directions of the transducer encounter exactly two elementaryturns of the composite winding, of opposite polarity and alternatelyarranged on each of the two narrow strips of the transducer.Furthermore, the two narrow strips of the transducer are at a sufficientdistance from the two internal and external ortho-radial branches of theconductive patterns of the wide strip of the target. Under theseconditions, the coupling of the conductive patterns 149 _(j) of the widestrip of the target on the measurement at the terminals of the compositewinding results from the combination of the induction of the conductivepatterns 149 _(j) on the secondary 253 (one narrow strip) and from theinduction of the conductive patterns 149 _(j) on the secondary 255 (theother narrow strip), these two contributions compensating each othersubstantially regardless of the position of the target with respect tothe transducer. The parasitic coupling then adopts a relatively stablevalue when the position of the target with respect to the transducerchanges. Furthermore, the coupling adopts a substantially zero valuewhen the secondaries 253 and 255 (narrow strips) comprise 2(N+1) turnsof alternating winding directions, as described for the sensor in FIG. 3for example, in order to make a spatially differential measurement. Afurther formulation consists of considering that, when the position ofthe target with respect to the transducer changes, the reading made by asecondary of the narrow strip of the transducer of the set of conductivepatterns associated therewith on the target is substantially “in phase”with the reading made by the secondary of the other narrow strip of thetransducer of the set of conductive patterns associated therewith on thetarget. Moreover and when the position of the target with respect to thetransducer changes, the reading made by a secondary of the narrow stripof the transducer of the set of conductive patterns 149 _(j) of the widestrip is substantially “in phase opposition” with the reading made bythe secondary of the other narrow strip of the transducer of the sameset of conductive patterns of the wide strip of the target. As such,when the two measurements are added by mathematical or electrical means(for example by a serial electrical connection), the parasitic couplingadopts a substantially zero value when the secondaries of each narrowstrip are designed for this purpose, whereas the wanted signal isretained and/or amplified.

It should be noted that, in the case of the serial electrical connectionof the secondary winding of a narrow strip with the secondary winding ofthe other narrow strip, and so as to obtain the features of the sensorsdescribed with reference to FIG. 2E, it is for example possible toselect as the midpoint of the composite winding, the serial connectionpoint of the two elementary windings.

It should be noted that further methods for combining the measurementsof the two secondaries of the narrow strip can be envisaged, such aslinear combinations of the signals conditioned separately, or furthermethods for electrically interconnecting the secondaries, with forexample the same aim of increasing the robustness of the measurements atthe wide strip and/or the narrow strips of the transducer, topositioning defects of the target with respect to the transducer.

It should be noted that in the examples shown in FIGS. 23, 25, 26 and27A, one of the elementary patterns of electrical period 360°/(N+1) isapproximately centered on the same angular position as one of theelementary patterns of electrical period 360°/N. For example, in FIG.25, the pattern 131 ₁ is centered on the same angular position as thepattern 129 ₁, and in FIG. 27A, the pattern 151 ₁ is centered on thesame angular position as the pattern 149 ₁. This configuration ispreferential as it helps increase the overall level of symmetry of thesensor, which particularly makes it possible to facilitate themanufacture and visual inspection of the target, or facilitate thedesign and manufacture of the sets of secondary windings. Theembodiments described are however not restricted to this particularcase.

As a general rule, it should be noted that the embodiments describedabove can be adapted to two signals θ_(N1) and θ_(N2), N1 and N2 beingdifferent integers but the difference thereof not necessarily beingunitary. Under these conditions, a sensor characterized by N1 andN2=N1+2 and of a similar arrangement to the arrangement of the sensorsin FIGS. 23, 25, 26 and 27A to 27C, makes it possible to extend theabsolute measurement over a range D_(tot)/N=180°. As a more generalrule, a sensor characterized by N1 and N2=N1+r, where r is a positiveinteger, different to zero and strictly less than N1 (in other words,less than or equal to N1−1), makes it possible under certain conditionsto extend the absolute measurement over a range D_(tot)/r=360°/r.

Furthermore, alternatively in the examples in FIGS. 26 and 27A to 27C,instead of reducing the width of the patterns of periodicity 360°/(N+1)with respect to the width of the patterns of periodicity 360°/N, itcould be envisaged to reduce the width of the patterns of periodicity360°/N with respect to the width of the patterns of periodicity360°/2(N+1).

Furthermore, it should be noted that the number of pole pairs ispreferably even for the patterns of the wide strip, so as to benefitfrom increased symmetry of the transducer on either side of the midpoint(particularly when the transducer is embodied according to the secondaspect).

Moreover, it should be noted that the embodiments described withreference to FIGS. 23 to 27C do not merely be applied to planar angulardisplacement sensors, but can be applied to further types of inductivedisplacement sensors, and particularly planar linear displacementsensors, or non-planar angular displacement sensors, for example lineardisplacement sensors “wound” (for example shaped according to acylinder) about and facing a part in rotation whereon on a target alsoof the linear type and “wound” (for example shaped according to acylinder). These two examples of embodiments are in no way restrictive.

Fourth Aspect

Generally, the target of an inductive displacement sensor consists of ametal plate cut over the entire thickness therefore so as to retain,facing the windings of the transducer, only portions of the platecorresponding to the conductive patterns of the target, as shown forexample in FIG. 50 of the patent EP0182085 mentioned above.Alternatively, the target can consist of a dielectric substrate, forexample a plastic plate, wherein one face oriented toward the transduceris partially coated with a metal layer forming the conductive pattern(s)of the target.

The targets of the type mentioned above have however points of weakness,which can pose problems in some applications, particularly applicationswherein the movable parts for which it is sought to be able to detectthe displacement are liable to be subjected to significant shocks orvibrations. Of these points of weakness, the inventors particularlyidentified the conductive patterns when they are relatively fine and/orangular, and the dielectric substrate which is generally soft (PCBepoxy, plastic, etc.). Furthermore, the embodiment of a firm attachmentbetween the target and a movable part for which it is sought to be ableto detect the displacement can pose difficulties. This attachment (forexample by bonding, screwing, fitting, etc.) can particularly representa point of mechanical weakness. Such points of weakness restrict theindustrial applications of sensors equipped with such targets, andparticularly require either instrumentation of the rotary mechanicalpart after the assembly operations of said part particularly when theseassembly operations are performed using force tools such as mallets andpresses, or protection of the target and/or the transducer in a solidmechanical housing. This is for example the case of instrumentedbearings which are embedded with high-tonnage press means.

According to a fourth aspect, it would be desirable to be able to availof an inductive displacement sensor target remedying all or part of thedrawbacks of existing targets, particularly in terms of strength.

For this, according to a fourth embodiment, it is envisaged to embody aninductive displacement sensor target, formed from one conductive metalpiece (for example a piece of steel), or one-piece target, machined suchthat the face of the target intended to be oriented towards thetransducer comprises one or a plurality of metal studs projecting from abase metal wall. The stud (s) of the target correspond to the conductivepattern or to the conductive patterns of the target, and the portions ofthe base wall not topped with a stud correspond to conductivepattern-free zones of the target, i.e. zones usually non-conductive inconventional inductive displacement sensor targets.

FIG. 28 is a perspective view representing an example of an embodimentof such a one-piece target 301, for an inductive displacement sensor.The target 301 has the general shape of a metal disk, machined such thatone face of the disk intended to be oriented towards the transducercomprises N conductive studs 307 _(i) (N=6 in the example shown)substantially of the same height, projecting from an approximatelyplanar base wall 309. Each stud 307 _(i) has a vertex or a top face,approximately planar and parallel with the wall 309. Furthermore, inthis example, the side walls of the studs are approximately orthogonalto the wall 309. The top faces of the studs 307 _(i) of the target 301define the conductive patterns of the target. In this example, thetarget 301 has a conductive pattern substantially identical to that ofthe target in FIG. 3B, i.e., in projection along an orthogonal directionto the median plane of the disk, the studs 307 _(i) have substantiallythe same shape and are arranged substantially in the same way as theconductive patterns 117 _(i) of the target in FIG. 3B.

The operating principle of the target 301 is similar to that describedabove, i.e. when the target is placed in front of a transducer emittinga magnetic excitation, induction phenomena, for example eddy currents,arise in the studs 307 _(i), particularly at the top face of the studs,inducing a variation of an output signal level of the transduceraccording to the position of the studs 307 _(i) with respect to thetransducer.

It should be noted that in the target 301, the portions of the surfaceof the target facing the transducer situated between the studs 307 _(i)are conductive. Consequently, under the effect of the magneticexcitation generated by the primary winding, induction phenomena, forexample eddy currents, can also arise in these portions of the target,at the base wall 309. As a more general rule, and for example in thecase of the sensor in FIG. 28 where the studs are in uniform electricalcontact with the substrate of the target characterized by the wall 309,the electromagnetic field distributions results from the overallinteraction of the conductive structure of the target with the magneticexcitation generated by the primary. In particular, there areelectromagnetic phenomena associated with the overall conductivestructure of the target rather than that of each conductive stud, forexample the flow of an induced current substantially along a loopconcentric with the axis of rotation of the target, rather than alonglocal loops substantially defined by the surfaces of the contracts 307_(i) or by the portions of surface of the wall 309 which are containedbetween the studs. It should be noted in particular that in the priorart, it is conventional to remove the base wall 309 as much as possibleand electrically insulate the studs 307 _(i) so as to avoid theseparasitic induction phenomena.

However, the distance between the transducer and the wall 309 beinggreater than the distance between the transducer and the studs 307 _(i),the induction phenomena arising in the wall 309 are less than theinduction phenomena arising at the surface of the studs 307 _(i). Thetests conducted by the inventors demonstrated that the inductivecontribution of the wall 309 can optionally cause a modification such asan attenuation or a modification of the linearity characteristics of thewanted output signal of the transducer when the height of studs 307 _(i)is low, but, on the other hand, it does not degrade the precision of theposition measurement which can be made by the sensor.

It should be noted that according to the first aspect, described inparticular with reference to FIGS. 12A to 12D, it is possible toenvisage, with geometric adjustments of the target and in particularwith the adjustment of the height of the studs 307 _(i) in the sensor inFIG. 28, adjusting the optimal target-transducer distance d_(opt) interms of linearity. As such, the height of the studs can be chosen suchthat the distance d_(opt) is compatible with the target application, forexample between 0.5 and 1.5 mm, which is a range of values compatiblewith various industrial applications.

By way of non-restrictive example, the height of the studs 307 _(i) isbetween 0.1 and 30 mm and preferably between 1 and 10 mm.

More generally, any type of inductive displacement sensor target withone or a plurality of conductive patterns can be embodied in one-pieceform, as described with reference to FIG. 28, for example inductivelinear displacement targets, or planar inductive angular displacementsensor targets having different conductive patterns from that in FIG.28, i.e. for example different from angular sectors or rectangles, andfor example characterized in that at least one of the contours thereof(for example the external contour) develops substantially like a spiralaccording to the angle on the target, or in that at least one of thecontours thereof develops substantially sinusoidally according to theangle on the target.

By way of illustration, a further non-restrictive example of a one-pieceplanar inductive angular displacement sensor target 401 is shown in FIG.29.

As in the example in FIG. 28, the target 401 has the general shape of ametal disk, machined such that one face of the disk intended to beoriented towards the transducer comprises conductive studs 407substantially of the same height, projecting from an approximatelyplanar base wall 309. As above, each stud 407 has a vertex or a topface, approximately planar and parallel with the wall 309, and the sidewalls of the studs are approximately orthogonal to the wall 309. The topfaces of the studs 407 of the target 401 define the conductive patternsof the target. In this example, the target 401 has conductive patternssubstantially identical to those of the target in FIG. 27A, i.e., viewedfrom above, the studs 407 have substantially the same shape and arearranged substantially in the same way as the conductive patterns 147_(i) of the target in FIG. 27A.

The embodiment of one-piece targets of the type mentioned above can beperformed by any known means for machining a solid metal part, forexample by etching, by sintering, by molding, by embossing, etc.

One advantage of the one-piece targets of the type mentioned above isthat they are particularly robust with respect to existing targets, andcan as such be handled without special precautions. This robustnessparticularly stems from the fact that such targets are solid and have noapparent points of weakness. Furthermore, these targets are easier toattach firmly to movable parts than existing targets. In particular, anymetal-on-metal force-fitting and/or metal-metal welding techniques canbe used. These two features make it possible to pre-instrument a verylarge majority of rotary metal parts even before the assembly thereof oruse in the host system. To finalize the instrumentation of the system,it is simply necessary to mount the transducer opposite the assembledtarget, either at the end of assembly or at any stage of the life-cycleof the host system.

According to one particularly advantageous embodiment, a one-pieceinductive displacement sensor target of the type described above can bemachined directly in a metal part for which it is sought to be able todetect the position (and/or the displacement), for example:

for an angular measurement, a motor vehicle steering column, an engineshaft or a reduction gearbox (for example at one disk-shaped face of anend section of the shaft), a rotary ring (internal or external) of aball bearing, a gear, etc.; or

for a linear measurement, a piston rod, a shock absorber body, etc.

Various examples and embodiment with various alternative embodimentshave been described above. It should be noted that those skilled in theart will be able to combine various elements of these various examples,embodiments and alternative embodiments without exercising inventiveskill. It should be noted in particular that the first, second, thirdand fourth embodiments described above can be implemented independentlyof one another or combined fully or in part according to the needs ofthe application.

The invention claimed is:
 1. A target for an inductive displacementsensor, the target comprising: a plurality of separated conductivepatterns distributed along a zone having a dimension D_(tot) in adirection of a first circular annular strip or a wide strip of thetarget, said patterns being defined by an overlay of at least a firstset of elementary periodic patterns having a period approximately equalto D_(tot)/N, including N first elementary conductive patterns of adimension approximately equal to D_(tot)/2N in said direction, regularlydistributed along the first circular annular strip of the target, eachof the first elementary conductive patterns having the shape of a sectorof the first circular annular strip of the target, and a second set ofelementary periodic patterns having a period approximately equal toD_(tot)/(N+r), including N+r second elementary patterns of a dimensionapproximately equal to D_(tot)/2(N+r) in said direction, regularlydistributed along a second circular annular strip or narrow strip of thetarget, concentric with the first circular annular strip and included inthe first circular annular strip, each of the second elementary patternshaving the shape of an annular sector of the second circular annularstrip of the target, where N is an integer greater than or equal to 2and r is a positive integer, different to zero and less than or equal toN−1, wherein first and second elementary conductive patterns overlap atleast partially.
 2. The target for the inductive displacement sensoraccording to claim 1, wherein the first and second elementary conductivepatterns have respectively the shape of portions of overlaid first andsecond strips parallel with said direction.
 3. The target for theinductive displacement sensor according to claim 2, wherein the firstand second strips are of separate widths, the first strip being at leasttwo times wider than the second strip.
 4. The target for the inductivedisplacement sensor according to claim 1, wherein N is an even number.5. The target for the inductive displacement sensor according to claim1, wherein said patterns are defined by the overlay of the first andsecond sets of periodic elementary patterns, and of a third set ofperiodic elementary patterns having a period approximately equal toD_(tot)/(N+r), comprising N+r third elementary patterns of a dimensionapproximately equal to D_(tot)/2(N+r) in said direction, regularlydistributed along said zone with an offset of approximatelyD_(tot)/2(N+r) with respect to the elementary patterns of the second setof periodic patterns, first and third elementary conductive patternsoverlapping at least partially.
 6. The target for the inductivedisplacement sensor according to claim 5, wherein the first, second andthird elementary patterns have respectively the shape of portions offirst, second and third strips parallel with said direction, both thefirst and second strips, and the first and third strips, being overlaid,and the second and third strips being approximately of the same widthless than the width of the first strip.
 7. The target for the inductivedisplacement sensor according to claim 1, wherein said direction is acircular direction.
 8. The target for the inductive displacement sensoraccording to claim 7, wherein said dimension D_(tot) is an angulardimension equal to 360°.
 9. The target for the inductive displacementsensor according to claim 1, wherein r is equal to
 1. 10. A transducerfor an inductive displacement sensor, the transducer comprising: aprimary winding producing a uniform magnetic excitation in a firstcircular annular strip of the transducer identical to a first circularannular strip of a target, facing the first circular annular strip ofthe target; a first set of at least two secondary windings eachcomprising N first turns of the same winding direction or 2N first turnsof alternating winding directions, regularly distributed along a zonehaving a dimension D_(tot) in a direction, each first turn having adimension in said direction approximately equal to D_(tot)/2N of thefirst circular annular strip of the transducer, and the N or 2N firstturns of each winding being regularly distributed along the firstcircular annular strip of the transducer; and a second set of at leasttwo secondary windings each comprising N+r second turns of the samewinding direction or 2(N+r) second turns of alternating windingdirections, regularly distributed along said zone, each second turnhaving a dimension in said direction approximately equal toD_(tot)/2(N+r) of a second circular annular strip of the transducer,identical to a second circular annular strip of the target and facingthe second circular annular strip of the target, where N is an integergreater than or equal to 2 and r is a positive integer, different tozero and less than or equal to N−1, wherein first and second turnsoverlap at least partially.
 11. The transducer for the inductivedisplacement sensor according to claim 10, wherein the first and secondturns have respectively the shape of portions of overlaid first andsecond strips parallel with said direction.
 12. The transducer for theinductive displacement sensor according to claim 10, further comprisinga third set of at least two secondary windings each comprising N+r thirdturns of the same winding directions or 2(N+r) turns of alternatingwinding directions, regularly distributed along said zone with an offsetof approximately D_(tot)/2(N+r) with respect to the second set, eachthird turn having a dimension approximately equal to D_(tot)/2(N+r) insaid direction, and first and second turns overlapping at leastpartially.
 13. The transducer for the inductive displacement sensoraccording to claim 12, wherein the first, second and third turns haverespectively the shape of portions of first, second and third stripsparallel with said direction, the first and second strips being overlaidand the first and third strips being overlaid.
 14. The transducer forthe inductive displacement sensor according to claim 12, wherein thesecond and third secondary windings are connected in series.
 15. Thetransducer for the inductive displacement sensor according to claim 14,wherein a serial connection point of the second and third secondarywindings is connected to an electrical connection terminal.
 16. Aninductive displacement sensor comprising: a target, the targetcomprising a plurality of separated conductive patterns distributedalong a zone having a dimension D_(tot) in a direction of a firstcircular annular strip or wide strip of the target, said patterns beingdefined by an overlay of at least a first set of elementary periodicpatterns having a period approximately equal to D_(tot)/N, including Nfirst elementary conductive patterns of a dimension approximately equalto D_(tot)/2N in said direction, regularly distributed along the firstcircular annular strip of the target, each of the first elementaryperiodic patterns having the shape of a sector of the first circularannular strip of the target, and a second set of elementary periodicpatterns having a period approximately equal to D_(tot)/(N+r), includingN+r second elementary patterns of a dimension approximately equal toD_(tot)/2(N+r) in said direction, regularly distributed along a secondcircular annular strip or narrow strip of the target, concentric withthe first circular annular strip and included in the first circularannular strip, each of the second elementary patterns having the shapeof an annular sector of the second circular annular strip of the target,where N is an integer greater than or equal to 2 and r is a positiveinteger, different to zero and less than or equal to N−1; and atransducer comprising a primary winding producing a uniform magneticexcitation in a first circular annular strip of the transducer identicalto the first circular annular strip of the target, facing the firstcircular annular strip of the target, a first set of at least twosecondary windings each comprising N first turns of the same windingdirection or 2N first turns of alternating winding directions, regularlydistributed along the zone having the dimension D_(tot) in the directionof the first circular annular strip or the wide strip of the target,each first turn having a dimension in said direction approximately equalto D_(tot)/2N of the first circular annular strip of the transducer, andthe N or 2N first turns of each winding being regularly distributedalong the first circular annular strip of the transducer, and a secondset of at least two secondary windings each comprising N+r second turnsof the same winding direction or 2(N+r) second turns of alternatingwinding directions, regularly distributed along said zone, each secondturn having a dimension in said direction approximately equal toD_(tot)/2(N+r) of a second circular annular strip of the transducer,identical to the second circular annular strip of the target and facingthe second circular annular strip of the target, where N is an integergreater than or equal to 2 and r is a positive integer, different tozero and less than or equal to N−1, wherein first and second turnsoverlap at least partially, and wherein first and second elementaryconductive patterns overlap at least partially.